1

Hello everyone,

I’m Anmol Vashishtha, one of the shortlisted candidates for BARC-OCES 2022.

I cleared the written test with a score of 136.35, the cutoff this year was 134.36. This year 99 candidates were shortlisted for interview out of which 5 have been shortlisted. I appeared for interview on 20th June at BARC, Mumbai.

Interview:

The interview panel consisted of 6 members.

After being seated, I was asked a little about my college and my final semester exam/presentation(as I am in final semester). Then, one of the members asked me “Have you prepared all the subjects from GATE syllabus only?”. I replied “yes sir”.

He then proceeded “But why GATE only? when you have been taught other subjects in college?”.

I replied: “Sir, because I’ve given GATE exam recently and it was also my second attempt, so these are the subjects that I have been thoroughly studying for two years”

He seemed to be satisfied by my response. He then asked me to stand up and write the 5 subjects I had prepared on the corner of the black board. I wrote OS, TOC, CN, DBMS, C.

A panel member asked: “Why have you not written DS and Algo?”

I replied sir:” Sir, I’m more interested in theoretical subjects, and DS and Algo don’t interest me much”, even they were surprised

The member continued: “ but you know right, that these subjects are a very integral part of Computer Science”

I replied : “yes sir I very much understand. I have a strong foundations of these subjects as I have prepared for GATE but when I go the interview call, I took that as an opportunity to dive deeper into these( the ones written on the board), so I have prepared for these only.”

The panel somewhat went along with it. And my interview starts from here.

OS:

OS panel member: “what are the functionalities of OS?”

Me: told about process management, resource allocation, memory management, I/O devices

OS panel member: “so you’ve told process management, what do you mean by a process?”

Me: told the standard definition i.e. “process is a program under execution”

OS panel member: "when do we call something a process? I mean like we have programs right, when does a program turn into a process?”

Me: elaborated the process of loading a program into main memory from the secondary memory and then tried to explain that these programs become processes when they are allocated main memory resources.

OS panel member: “while explaining you mentioned the word interrupt, what do you mean by an interrupt?”

From this point on the entire OS section shifted towards interrupts, so this discussion consisted more of concepts of Interrupts as covered in Computer Architecture rather than OS but luckily interrupts was a topic that I had put a little extra effort while preparing for GATE . I’ll summarize the series of cross questioning.

• what is an interrupt
• what happens when an interrupt occurs? I told about the mechanism and Interrupt Vector Table and Service Routines.
• How do we know what to do when an interrupt has occurred? told about the vectored interrupt mechanism
• How does the OS know that an interrupt has occurred? told about the control signal mechanism, the INTR lines etc
• Why do we need interrupts in the first place? told about privileged instructions and kernel mode execution
• Little cross questioning on kernel mode and why some instructions are declared as privileged
• What’s the difference between interrupts and exceptions?

At last the OS part was completed.

C:

Then they shifted to C. I faltered a little in this section but the panel members gave ample hints and time for me to identify my mistakes and to rectify them.

C panel member: “write a program that accepts an alphanumeric string and extract the number in it, for example if the string is ‘a2b3cd4’ your code should return the number 234”

Me: Before writing anything I preferred to verbally explain my thought process. “Sir we would iterate through the string and whenever we encounter a number we would extract it and store it as an intermediate result”. Then I started writing the code. Whenever I was stuck I used to quickly take a sample input and dry run my code, this helped me find all errors immediately.

C panel member: "how will you handle negative numbers?"

Me: told that we can add a check and then make the number negative after processing the string.

C panel member: "what can be the maximum size of a number that can be extracted by this code?"

Me: I wasn't able to provide a satisfactory answer, but I tried to answer in all ways I could.

TOC:

Then they shifted to TOC.

TOC panel member: "what are the uses of finite state automata?"

Me: described a little about FSA, then the only example that struck my mind was the LR(0) item set. How FSA is used to track what productions have been scanned. Eg -> S -> A.B, S-> AB.

TOC panel member: "you've mentioned parsing and grammars, where else is FSA used in compilers?"

TOC panel member: "Can you design a FA for accepting integer declarations? For example int abc;"

Me: I wrote the Regular expression first and then proceeded to draw the FA, followed by a bit of cross questioning on FA and parsing in general.

After this they asked few questions from the remaining Subjects. I'll summarize them:

• DBMS:
• What all topics have you learnt? Told Transactions, Normalization, Indexing etc
• How are transactions implement isolation? I told them about view and conflict serializability but the member was expecting the isolation levels. I said I cannot recall those at the moment.
• Why do we need Normalization? Give examples
• What are types of relation in DBMS? Told one to one , many to one etc
• Give example of each
• Kind of data structures are used in DBMS? Thought for a moment and told hash tables, B tree etc
• Explain B trees and Hash tables?
• How collisions are resolved ? What do you think is better for collision resolution in general? Thought for a bit and said that I would prefer linked list approach because in worst case if insertions are made to same slot again and again LL approach would not affect the rest of the hash table, while inserting into successive slots would affect the rest of hash table as well.
• Data Structures:
• Write declaration of LL
•  How would you find the middle element? Told about the brute force solution to scan and count the number of nodes and traverse again till n/2 elements
• Can you do it in single traversal? Told about the double pointer approach and moving one pointer twice as fast as other.
• Computer Networks:
• What is subnetting?
• Why do we need subnetting? I felt that I couldn't provide a satisfactory answer to this, but again I tried to explain my best.
• You've explained subnetting, now explain Supernetting, why do we need supernetting? Again I felt that I couldn't provide a convincing answer but I explained that "contrary to subnetting, when an organization wishes to combine two or more networks to achieve a higher level of logical abstraction. I told them an example that for example an institution had an ML and Neural Network departments, so it can combine these n/w to form a supernet and logically designate it as Artificial Intelligence department".
• Java:
• DS panel member asked whether I was familiar with C++ and OOPs. I replied that I have learnt Java rather than C++.
• DS panel member: tell me about OOP concepts?
• DS panel member: tell me about Polymorphism, how is it achieved in Java? Told but I got confused in Method overloading and overriding. But I corrected my mistake after getting a hint.

Then the last question I was asked was from TOC again.

TOC panel member: "how can you implement DFAs in C?"

Me: told about the matrix approach

TOC panel member: "What if we don't know about the number of stated beforehand?"

Me: Thought for a bit but couldn't answer properly

Then my interview concluded, I greeted them and came out of the room. My interview went for about 1 hour and 23 minutes.

Preparation:

Written Test: Just revised my GATE notes ( I have attended Made Easy Online Coaching) and for practice I combined all the previous year Gate 1 marker questions in a single pdf. I used to solve all these and then evaluate my performance.

Interview: Reading through past interview experiences on GATE Overflow, Quora etc, I realized that revising notes wouldn't be enough. So I turned towards university lectures available on YouTube. I used to watch a lecture and then go through the corresponding topic from a standard textbook. This was naturally time consuming so I limited myself to important topics of each subject. I'll summarize the resources:

I wish all the future aspirants best of luck for all their endeavors.

2
Had a written test, based on which I was called for interview.

Round 1:

P1: Find value of i^i, explain your approach.

P2: A numerical question related to dependent variables, don’t remember the exact question.

P3: Explain Selection Sort, and maximum number of swaps in Selection Sort.

P2: Given a column vector A, what is rank of AA’?

P2; What is the maximum and minimum possible rank of a matrix consisting of N k-D vectors? What are the assumptions involved in each case?

Round 2:

P1: Explain your background with ML/AI.

P2: Explain any one project on AI that you worked on.

P3: Why MTech RA?

P2: Explain why residual connections allow deeper networks. What happens in deep networks without residual connections?

P2: How do you decide Hyperparameters like Learning rate or number of layers when training neural networks?

P1: Which subfield of AI are you interested in?

Result: SELECTED!
3
There was a written test for self sponsored category of AI and CSE on 24th June 22. I got shortlisted for both of them. My interview was on 25th June 22.  My interview was scheduled at 12 but after waiting almost 1.5 hr, they admitted me into the WebEx meeting... So the questions were :

1. Did u sit for placement?

I denied. They asked me the reason. I told them i was quite focused on gate only so didn't get much time for placements.

2. Graduated in which year, which stream and which college?

3. Do you know programming? If yes, write a code to find palindrome of a number without converting into a string.

4. Given two matrix , write code to multiply them

I tried but couldn't do that. So they gave me values of A and B matrix and told me to find answer of A*B mathematically. I did.

5. Do you know data structures? What are the types of data structures?

I told them all data structures

6.. how to convert stack into queue?

I told them to use two stack..pop from stack 1 and push to stack 2. Then later pop from stack 2, you will get the queue.

7. What is ur preference? ai or cse?

I told them that it's cse.

They asked me why not AI?

I told them my reasons

And the interview ended!!!
4

My interview was on 27th June 2022. The interview panel had 2-3 interviewers. The questions asked were:

1. Introduce yourself.   : I introduced myself and also stated at the end that my fav subjects are DS and Algo.
2. They asked me if i m comfortable with probability. I said that I haven't done that in depth but they still can ask. They said that they wont ask on probability then.
3. They said “Let me ask very basic questions which you have learnt in high school. I will give you equations and you have to find of the values as well as plot graphs.
4. They gave me 3 equations.
5.  y =  |x|
6. |x|+|y| =1
7. x+y=1

I drew the graphs and explained the logic to them. Also i showed them the graph drawn in front of camera. They told me to name the x and y axis.

Then they shifted to linear algebra

1. Given a system of linear equations Ax=B, what are the cases when we get unique, no solution and infinite many solution?    ; I explained them the geometric aspect that solution will be the point where the lines will intersect.
2. What do you mean by homogeneous and non homogeneous equations?

When will you say that the solution is unique or infnitely many Mathematically? ;; I told them the rank concept.

And so the interview ended

Never thought that they will ask so many basic questions. But if you have a good command over maths, then you can ace  the interviews.

5

Initially for MINDS(IITD) or CMINDS(IITB) there was a written test, if you qualify then you will proceed to the interview round.

You can follow the link given below for the syllabus. As both the written tests (no -ve marks) was more or less the same:

https://bit.ly/3Or8Nrw (IITB CMINDS)

In IITD there were 3 coding questions in addition to MCQs & MSQs and the test was conducted on HackerEarth platform.

IITD Interview Questions and Resources:

Around 40 people were shortlisted for the interview.The interview was conducted on 3rd June 2022(Till that time 3 coap rounds were over).My interview was scheduled at 4pm on Microsoft Teams.In my panel there were 3 professors.Each professor asked me questions from different subjects(given below).And the interview lasted for around 40-50 mins.

General Questions:

2. Currently what offers do you have?If you get M.Tech will you consider it or stick to MS(R) program and Why?

3. What are your favorite subjects? (Best answer, Linear Algebra & Probability for AI and Data science profile interviews.)

Also go through basic AI/ML stuff. Resource: https://bit.ly/3xy4tzO

Linear Algebra:

Take an equation Ax=B

1. Explain the solution of the system of linear equations w.r.t column space?

2. When will the system have a solution?

3. If matrix A has full rank, then for what B vectors does the system have a solution?

4. If the B vector doesn’t lie on the column space of A then how to get an approximate solution(projection concept)?

Resources:

https://bit.ly/3Qza41C (Must read upto 23rd video)

https://bit.ly/3xIokMP (Alternative to above resource)

Calculus:

1. What is a convex function?(Read thoroughly about concave & convex functions).

2. What is gradient?Give its geometrical significance.

3. What's a directional derivative?

Resources:

https://bit.ly/3zOvvpc

Probability & Statistics:

1. What is covariance for 2 random variables x & y?

2. Proof that for independent random variables covariance is 0.

3. Prove E(x+y)=E(x)+(y) for both independent & dependent cases.

4. Prove E(xy)=E(x)E(y) for an independent case.

5. A coin is tossed n times we define a random variable as follows,where xi is ith coin toss, prob. of head in each toss is p(success):

Find E(x(bar)) and Var(x(bar)).(Use linearity of expectation concept)

Also do read thoroughly joint pdf,pmf, conditional expectation,total expectation,CDF etc.

Resources & Tips:

Keep handy all the distributions equations and graphs,specially normal distribution and approximation of poisson & binomial distributions using normal distribution.

Also go through proof of the memoryless property of geometrical & exponential distribution.

Recommended videos:

https://bit.ly/3OtYFhK (Must read upto 98th video)

https://bit.ly/3OoqmbC (Sampling distribution concept)

https://bit.ly/3n1d499

https://bit.ly/3OaaZ6O

https://bit.ly/3HBPE3G (Just go through week 3 important set of problems)

Algorithm:

1. Suppose you need to climb a stair of n steps and you can take at a time 1 step or extend your leg and take 2 steps or 3 steps at a time.Finds number of ways you can climb n steps.

(Hint: Take sol. as T(n).For T(n) we have 3 tree branches T(n-1)(taking 1 step at a time)/T(n-2) (taking 2 steps at a time)/T(n-3) (taking 3 steps at time) then again solve the subproblems of size (n-1)/(n-2)/(n-3) )

Verdict: Selected (IITD)

Note:

1. If you have a 650+ Gate score(Gen) you should definitely prepare well ahead as you will most probably get a call.Applicable for all branches.

2. IITB focuses more on LA & Prob.(specially joint distribution which was not part of the GATE syllabus).You have to study beyond the GATE syllabus.

3. You should never go out of studies after GATE for a long time else it will be difficult for you to crack the interviews.

4. Must be prepared with the B.Tech final year project.

Best of Luck for your selection :)

6
I was selected for an interview by Standing Committee, therefore I didn’t have to give PGEE and my GATE wasn’t considered. In case anyone wants to know, my GATE (2021) score was 627.

The interview panel had 3 professors.

P1: Current role, past research experience, past research topics.

Me: Told

P2: Explain Vector Spaces

Me: Told

P2: What is dot product? What is its significance?

Me: Told

P2: What is the rank of a matrix? What happens if a vector is multiplied by a matrix with rank lower than its no. of dimensions?

Me: Told

P2: What are basis vectors?

Me: Told

P2: Given N vectors in N-d space, how would you find N perpendicular vectors using the given vectors?

P1: Given a graph, is the shortest path between 2 vertices always included in the MST?

Me: Told no using counter-example.

P1: Explain K-Means Clustering

Me: Told

P1: Explain Neural Clustering

Me: Didn’t know

P1: Explain any of your papers and the math involved

Me: Told

P3: What makes a neural network non-linear?

Me: Told

P3: What are the properties of a sigmoid activation?

Me: Told

P3: What is the derivative of sigmoid?

Me: Told

Result: SELECTED!
7
I got shortlisted for interview at IIT Hyderabad CSE via self sponsored mode. It was held on 13 June 2022. I had only revised DS-Algo and Maths. The interview consisted of 2 interviewers.

Person 1: Pls introduce yourself in 30 sec. Like your name, college name, favourite subjects, thesis name,project name etc

Me: (I told them abt myself)

Person 1: What was your thesis on? Can u explain it?

(I was completly unaware what thesis meant as in our college, we only did major project, so i told him that we only had major project and explained him that)

Person 1: Did you deploy your project?

Me: Yes I did

Person 1: As you told your favourite subject is algorithm, can u please tell me the time complexity to find 2 numbers in an unsorted array in such a way that those 2 number’s sum is target. Target will be given as input

Me: I first explained the naive method of O(n^2). Then i said that i will sort them and use 2 pointer method to find..tc= O(nlogn +n) ~ O(nlogn).

Person 1: Can you optimize it further? Have you heard of hashmap, can u optimize using that?

Me: I was pretty struck there..I tried doing it but couldnt do that. Later after the interview i realized that i already knew the method but due to the situation, i panicked and couldnt give the ans.

The ans was , take a element from the array, check if target-element is there in hashmap or not.. do this for every element.. searching in hashmap is O(1) .. thus tc = O(n)

Now person 2 started asking me question

person 2: Tell me the worst case complexity of quicksort

Me: I explained him the entire quicksort.

Person2: Suppose you are given median element using a certain algo which takes O(n) tc. will the time complexity be reduced

me: I told them the recurrance relation of quicksort using median as pivot .

And the interview ended. The results are awaited.
8

Hi Everyone!

This is Anmol Garg, I got a GATE CSE score of 749 (AIR 343) in 2022 and 742 (AIR 447) in 2021. I applied to IIT Bombay MS By Research program in CSE with my 2022 score, as I am a General candidate and knew I won’t be getting a direct offer from any top IIT.

The admission process is available here:

The process consisted of 2 rounds, 1st round being a written test on Codetantra (pen-and-paper based) and 2nd round being an Interview. I had chosen Computing Systems (CS) Stream for my test and interview.

ROUND 1 – WRITTEN TEST
---------------------------------------

As I had chosen CS stream, I had the option of attempting any 12 questions out of the following 3 panels:
1. Software Engineering, Compilers, Programming Languages
2. Systems Software
3. Hardware and Security

I mostly solved questions from Programming, DS & Algo, Computer Networks and Operating Systems.

Result :: SELECTED

ROUND 2 – INTERVIEW
---------------------------------

Before interview we were asked for our preferred stream (CS/TS/IS), and any RAP project (optional). I had chosen CS as my stream and Virtual Labs (https://docs.google.com/document/d/1op-KwA6B99WHKCoZOkMR3ULcIDPvvbboRWmBtT7QBNI/edit) project under Prof. Kameswari Chebrolu as RAP Project.

My interview panel consisted of Prof. Kameswari Chebrolu and Prof. Bhaskaran Raman

Initial questions were about my past projects and work experience, and the flagship projects I did when I was working.

I was then offered a choice between Computer Networks and Operating Systems as topic for Interview. I decided on Operating Systems as it is my strong suit.

OS questions were mostly from basics of Virtual Memory. I don't remember the exact questions, but some of them were like:

1. What is virtual memory?
2. In which cases is it used?
3. If you have an unlimited amount of storage, will virtual memory still be used?

After answering these questions, I was given a choice between TA & RAP. I chose RAP as the Virtual Labs project seemed very interesting.

As I have experience in Back-end and microservices development and deployment, I was mostly asked questions from that space. Some of the interesting questions were:

1. What is docker, and how does it work on a hardware level?
2. Suppose you are maintaining a set of microservices, and you notice they are getting slow. What steps will you take to mitigate it?
3. Do you know what AWS is?
4. What can be a real-world example of implementation of feedback queue. Give examples from projects you have done previously

After answering these questions, I was told that they were done, and I was free to ask them any questions. I asked questions about the project, such as:

1. What’s the current state of the project
2. If I join, at what state do I have to start work from (from scratch or not)
3. What technologies were being used
4. What’s the current timeline for this project

I learned that the project’s back-end is being built using Django, in which I have around 1.5 years of experience, so I told them about my experience and all the projects I have done in it. It was clear that they were impressed by it.

Then they asked me that if I were to be offered admission, will I join IITB or do I have any other preference, and if I do join IITB, will I prefer TA or RAP.

I again answered that IITB is my top choice and I would prefer RAP as I wanted to work on such a large scale problem.

Then the interview ended. It lasted for around 45 minutes.

Result :: SELECTED FOR RAP IN 1st ROUND

9
An interview was conducted with all the candidates who applied for Mtech CSE IIT Delhi.

I have given my interview experience below.

The panel consisted of 3 professors.

The 1st professor started off by asking about the subjects I am interested in. Since I mentioned Data Structures and algorithms, he started asking questions about them. The first question was about all pair's shortest path algorithms, the significance of k and whether the looping involving k is outside or inside the loop concerning the i and j nodes in dynamic programming formulation. The next question is on the usage of min-heap and union-find for obtaining a minimum spanning tree.

The 2nd professor asked about an approach to finding the median of an array. He told me to optimize the approach without sorting the array. I couldn’t come up with an approach to do it. Next, he asked me to assume such an algorithm exists and use it to come up with an optimum algorithm for the fractional knapsack problem. I couldn’t come up with an approach to do it too.

The 3rd professor asked a few questions on convolutions since I said I am interested in Computer vision which I answered completely.

The interview overall lasted for about 15-20 min. The professors were quite friendly and provided hints whenever I am stuck. They care more about the clarity of concepts rather than just plain answers.

Thank you
10

### 2021 GATE Overflow Interview Experience Links.

 College Name Interview Experience Blog Link Program Specialization BARC https://gateoverflow.in/blog/14029/barc-interview-experience-2021 M.Tech. CSE IISC https://gateoverflow.in/blog/13585/iisc-csa-mtech-reseach-interview-experience-2021 CSA M.Tech. Research CSE IISC https://gateoverflow.in/blog/13583/iisc-mtech-research-online-written-screening-test-questions CDS M.Tech. Research CSE IISC https://gateoverflow.in/blog/13558/iisc-research-interview-experience-printing-engineering CDS M.Tech. Research CSE IISC https://gateoverflow.in/blog/13540/iisc-bangalore-tech-course-work-written-test-questions-2021 CDS M.Tech. Research CSE IISC https://gateoverflow.in/blog/13537/iisc-bangalore-tech-course-work-interview-experience-2021 CDS M.Tech. Research CSE IISC https://gateoverflow.in/blog/13453/various-interview-questions-research-programs-iits-iisc-2021 CDS M.Tech. Research CSE IIT Bombay https://gateoverflow.in/blog/13421/iit-bombay-ms-intelligent-systems-interview-experience MS CSE IIT Bombay https://gateoverflow.in/blog/13453/various-interview-questions-research-programs-iits-iisc-2021 MS CSE IIT Gandhinagar https://gateoverflow.in/blog/13434/iit-gandhinagar-interview-questions-2020 M.Tech. CSE IIT Gandhinagar https://gateoverflow.in/blog/13356/iit-gandhinagar-mtech-regular-interview-experience-2021 M.Tech. CSE IIT Indore https://gateoverflow.in/blog/13596/iit-indore-interview MS CSE IIT Indore https://gateoverflow.in/blog/13476/iit-indore-ms-cse-interview-experience-2021 MS CSE IIT Indore https://gateoverflow.in/blog/13381/iit-indore-ms-research-cse-interview-2021 MS CSE IIT Jodhpur https://gateoverflow.in/blog/13532/iit-jodhpur-mtech-cse-interview-experience-self-sponsored M.Tech. CSE IIT Jodhpur https://gateoverflow.in/blog/13530/jodhpur-self-sponsored-with-fellowship-interview-experience M.Tech. AI IIT Kharagpur https://gateoverflow.in/blog/13597/iit-kharagpur-ms-interview MS CSE IIT Madras https://gateoverflow.in/blog/13430/iit-madras-ms-interview-experience MS CSE IIT Madras https://gateoverflow.in/blog/13423/iit-madras-ms-intelligent-systems-interview-experience MS IS IIT Madras https://gateoverflow.in/blog/13453/various-interview-questions-research-programs-iits-iisc-2021 M.Tech. CSE
11

Hello Everyone. I am Neelam Singh passed out in Aug 2021   from a private Engineering college in M.P Bhopal. I appeared for BARC written test in CSE on 25 Sept 2021 and interview on 11 Nov 2021 and by god grace ,I cleared the interview in  first attempt.

How I prepared?

I took guidance from Deepak Sir and Sachin Sir from GO classes. GO Classes helps me to clear my concepts and build my career . All the teachers explain in very detailed and nice manner and also have doubts classes at the end of every class. Sachin Sir and Deepak Sir are highly supporting ,knowledgeable and friendly. I will suggest every GATE and PSU aspirants to go through the free course of DM and C on GO Classes.You will love it .

For written test , I went through the notes of GO Classes and Applied Gate .For interview I refered GO classes notes(for C, DS,Algo) , Geeksforgeeks articles(for C,DS, Algo, DBMS) and GateBook notes for CN .

What all subjects I chose for Interview?

I chose C, DS, Algo , DBMS ,CN . But they also asked OS . They consider one programming language and OS as almost  neccessary  .

what all questions they asked ?

C

1.Write C program to merge two sorted arrays into one and return new sorted array.

2.Why you prefer C over other languages ?

3.Where global and static variables are stored ?

4.How will you return an array build inside a function? (Hint:- using malloc )

DS

1.State some uses of stack DS?

2.How System Stack works?

3.What all activation record contains?

4.What DS will you use to store variable length URL?

5.Write node structure for stack used for storing forward and backward links/URLs visited , while browsing?

6.How stack helps in storing /performing undo or redo operations on the URL visited?( Hint:- By maintaining 2 stacks )

7.Write code for push and pop in stack implemented using Linked List?

OS

1.What is OS?

2.What are all functionalities of OS?

3.What is process?

4.Draw process state diagram?

5.What happens when process is in new and end state in process state diagram?

6.What all resources are allocated to a process?

7.What PCB contains?

8.How PCB is implemented?

9.What is process synchronization?

10.How process synchronization is achieved ?

11.What is semaphore?

12.Write code for synchronization using semaphore?

13.How can 2 processes access same semaphore variable?

14.If suppose a process generate address corresponding to other process memory space , will it be allowed to access? If yes , How? if no, How?

15.What kind of addresses a process generate ?(Virtual or physical)

16.How much memory , a process think it have and it actual have and how mapping is done between two? (concept of virtual memory and pagetable ).

17.What is swap space?

CN

1.Explain how a process will send data to another process on host on another network ?x

2.How ARP protocol works?

DBMS

1.What is transaction?

2.State properties of transaction?

3.How isolation is achieved in transaction management?

4.What if we allow non-serial schedules?

5.What is normalization and explain its type?

6.Do normalization impact performance . If yes , How?

7.When should normalization be performed and when not?

ALGO

1.Suppose you are given a array, return N subarrays such that their sum (sum of elements of each subarray) difference is minimum . Suppose S1, S2,..Sn are n subarrays sum ,then |S1-S2| +|S1-S3|+….+|S1-Sn|+|S2-S3|+|S2-S4|+…. should be minimum . Give algorithm for it.

2.Give greedy algorithm for above problem?

TIPS:

1.Prepare one programming language and OS .

2.Explain in detailed manner, every question.

3.While preparing look at implementation side of every concept , espically in OS,DS.

4.Don’t mug up the concepts . Try GOClasses once.

12

Exam: Jan 2020

Shortlist for the interview: May 2020

now coming to my interview

Interview Experience :

Date of interview-  4th/March /2021

Venue- DOS,Delhi

Interview mode: Zoom call in ISRO center (thanks to covid)

Reporting Time- 8:30 AM.

My interview was started at approx 11:00 am.

After entering the interview hall, I was connected with 5 ISRO centers over ZOOM call(around 15-18 scientists overall)

Transcript notation -> <center> : <message/interaction>

• VSSC : Vikram Sarabhai Space Centre
• URSC : U R Rao Satellite Centre
• SAC : Space Applications Centre
• SDSC : Satish Dhawan Space Centre (He didn’t speak a word, but sir was observing entire interview)
• C1 : no idea which center it was

VSSC : Good morning!

Me : Morning sir.

VSSC : ok tell me the technologies you are comfortable with (no intro no nothing lol, straight to business)

Me: am comfortable with ML and AI and am currently doing masters in the same

VSSC : relation between two (answered)

VSSC : define Data analytics (answered)

VSSC : components of Data analytics ( sorry sir and end)

VSSC:  (looking at my bio-data form) here you have written you have worked on some IoT applications during your time in XYZ org.

Me : yes sir that was an Internship.

VSSC: Internship? we thought it was full-time(since the description was complex)

Me: Yes sir, I was responsible in so and so part of that project.

VSSC: makes sense, tell me your fav programming lang.

Me: am comfortable with C and python.

VSSC: python! very good.

VSSC: does python have arrays? (answered)

VSSC: the difference between list and arrays? (answered)

VSSC: over to you URSC

URSC: what does ‘&’ do in c? (answered)

URSC: ‘&’  can be used in before function and variables right, what’s the difference? (answered)

URSC: what is a union?

URSC: alright, suppose you have an integer array of 40bytes, you need to access it byte by byte, how will you do it? (told type casting approach)

they stressed on this question for few mins, I couldn’t come up with the approach they wanted and they finally said hint was the previous question(union), then I was like ahh. then they directly moved on to the next question, no answer and all.

VSSC: you must be comfortable with CPP also right since you know py and c?

Me: Am rusty in CPP but I can answer few questions. (MISTAKE)

VSSC: what does ‘&’ do in CPP? (ikr ‘&’ day lol)(answered)

VSSC: what’s the difference of ‘&’ in c and cpp(half answer)

VSSC: the difference between public, private and protected (messed up big time here :( )

VSSC: ok (I could feel that disappointment in their face)

VSSC: function aliasing in CPP?(answered but they went deep got stuck)

Here I ACKed that my CPP and OOPs are rusty

VSSC: No problem, it’s natural. (I was like wow)

finally, they asked fav subjects. told OS,COA and TOC

VSSC: Over to you C1

C1: What is zombie process(answered 2 times with example,they were not satisfied)

C1: the difference between file structure and data structure? (not answered properly, then they themselves gave out definitions)

C1: Where is the file structure stored and where is a data structure stored? (again with hint was able to tell)

C1: Types of message passing?(answered standard ones which are in Galvin but, they asked for more)

C1 was not happy with half of my answers, so I felt a bit low since OS was my fav subject.

C1 : we are done

VSSC : over to you SAC

SAC : What is LAN ? (answered)

SAC : How is it different from MAN and WAN? (told: distance and medium, he laughed )

SAC : Ok tell me the difference in the distance then (told but, interchanged MAN and WAN. he again laughed and said MAN is bigger than WAN, then I corrected it)

SAC : (Scrolling through my UG marks cards) define SAN (answered)

SAC : Types of SAN? (forgot)

SAC : What is NAS? (answered in short, he expected more)

SAC : Two simple questions regarding OSI (answered)

SAC : Ok am done (and laughed)

This laugh was messing around in my head. like I was only thinking “did I do that bad during C1? “(form here only downhill)

VSSC : super scalar processor ? (answered)

BIGGEST BLUNDER that led to my results ;-;

VSSC : Throughput of pipeline processor (a simple and basic question(I know) but, messed it up in follow up questions)

since my mind was playing with me I answered it so badly that even I wanted to punch myself in the face.

VSSC : Ok URSC over to you

URSC: what is coupling and cohesion? (answered)

URSC: we do ground testing of rocket software here and you might be aware of generic software testing, how is it different? (answered in a general sense, ma’am was satisfied)

URSC: Have you ever heard a language named as ADA? (I was like what??? then she asked which textbook did you read during advanced computer architecture, this was a subject in BE which I never read. so you know my reaction lol)

URSC: few more generic questions on CPP (I answered 4/6)

URSC: define hypervisor (told about layer but they were seeking actual definition)

URSC: We are done

VSSC: Thank you we are done

well, the interview lasted for 34mins there were ups and a lot of downs(lost focus in between). I knew that I was out but, after hearing few other interview exp from my friends I thought my questions were a bit tricky and had little hope that I might get In.

but in the end, I FAILED in getting into the merit list (not even waitlist, as expected. you can’t mess up a simple COA question) but had a lot of learnings from it.

Learnings :

- Every stuff is important, these experiences are just for reference, they know and ask everything in an interview(It’s like that saying “if you even have a single point of failure then you will fail”).

- Here they focus more on the quantity of topics covered, in-depth helps but, try to read extra stuff for your fav subjects.

- They see your BE marks card so know the basics of few subjects you covered in BE(especially 4th year ones).

- Whatever happens, keep your focus in the interview (else you will end up like me)

- Luck does matter a lot but it can be overridden by hard work along with practice (practice with others as much as possible)

well, this was my story/exp had a lot of fun giving this interview, I mean you see few scientists who come on TV during the launch(fanboy moment).

I have given a lot of private MNC interviews but never felt this happy. so this interview has its own class.

give your best! (One day I will get there, passion > money :P)

and congrats to the guys who made it in, you truly deserve it :)

13

Date: 20-07-2020

There are 5 interviewers in panel

Prof1 : (smiling) Devendhar right….?

Me : Yes sir

Prof1:  You from Telangana ?

Me: Yes sir

Prof1:  How are you? and is everything fine ?

Me : Im fine sir, thank you.

Prof1: How is the covid situation in your town?

Me: Now situtation is improving in my town sir and day by day becoming normal.

Prof1: I hope you and your family is safe ?

Me:  yes sir, thank you.

Me: Introduced Myself

Prof2: Programming question

Given a 2d matrix which contains 0's and 1's only, is there any row contains all 1's ?

They gave me a link of notepad and said me to write code in it.

Me :  I wrote

Prof2: Okay, Done with you.

Prof3: Which subject you chose ? (they gave me a link before the interview to choose the primary subject)

Me: OS sir

Prof3: What are the different scheduling algorithms?

Prof3: What is the pre-emptive scheduling algo?

Prof3: Given a problem (AT, BT), find avg TAT, WT using Round robin algo?

Prof3: What means TAT?

Prof3: How to choose appropriate Time quantum ?

Result : Selected

14

Hello Everyone !!!

The written exam happened on 12th Jan 2020 and the shortlist for the interview came on 9th May 2020. I was not much confident about the ISRO examination result but I got shortlisted for the interview.

Interview Experience :

Date of interview-  10th – March -2021

Venue- NRSC Guest House Conference Hall, Balanagar, Hyderabad.

Time- 8:30 AM.

In the big reception hall, everyone was asked to sit and wait for their turn. At appx. 8:30 AM, they verified the documents and covid report. Document verification was done. At 8:45 am they called me inside of another waiting room. I was waiting outside of interview hall.

My interview was started at approx 9:00 am :

As I entered the room there was a big table with big screen, and panel head (PH) was on the screen. then panel head asked me to sit.

PH : (smiling) Devendhar right….?

Me : Yes sir

PH:  You from Hyderabad (Telangana) ?

Me: Yes sir

PH:  How are you? and is everything fine ?

Me : Im fine sir, thank you.

PH: How is the covid situation in your town?

Me: Now situtation is improving in my town sir and day by day becoming normal.

PH: I hope you and your family is safe ?

Me:  yes sir, thank you.

Me: Introduced myself.

PH: Which programming languages you are comfortable?

Me: C, Java

PH: What is OOPs?

PH: What is Polymorphism ?

Me: Answered (but could not defined in proper way)

Then he asked one of the panel members to continue…

P1 :  what are your favourite subjects ?

Me: Data structures, Algorithms, Database and management system, Operating system.

P1: What are the functions of OS?

P1: What are IPC Mechanisms?

Me: Answered (I mentioned only few)

P1: Any other IPC mechanisms  than what you told ?

P1: What are various process states ?

P1: What is pre-emption?

P1: What are synchronization mechanisms ?

I answered all of them, then he moved to C

P1: What is Declaration and Definition of a variable? difference between them ?

P1: What is Postfix and Prefix?

P1: What is Structure and Union? Difference ?

I answered all of them, then he moved to Computer Networks

P1: LAN vs WAN ?

P1: What is Ethernet ?

P1: What is CSMA/CD and explain in detail?

P1: What is firewall and Why we use it?

P1: What is Denial of service attack ?

I answered and all of them, then he moved to Software Engineering

P1: What is SDLC and what are the phases ?

Me: I gave definition, bt he asked me explanation of each phase. Then I explained the each phase.

P1: What is whitebox testing and blackbox testing ?

Me: First, I gave definitions bt bt he asked me to explain. I explained.

Then he asked one of the panel members to continue…

P2:  Are you comfortable with compiler ?

Me: yes ma’am (with doubtful face bcz I didnt mentioned in fav subjects)

P2: Why compiler ?

P2: What are the steps in designing the compiler?

P2: What is interpreter and compiler? differences?

P2: Is compiler platform dependent ?

Me: I said yes

P2: If I compiled one program in one machine and can I run it on another machine or Do I need to compile again?

Me: Yes ma’am, need to compile again

P2: are you sure ?

Me: Yes ma’am

P2: really ??

Me: We can use cross compiler also ma’am.

P2: Ok… I’m done with you.

P3: you did project in Deep learning right ??

Me: Yes, ma’am

P3: What is neural networks ?

P3: What are different types of neural network connections ?

P3: Different types of learning algorithms?

P3: Which one is used in your project ?

P3: What is the benifit of Reinforcement learning ?

P3: What is Activation function ?

P3: How you say it converges and when you stop ?

Me: answered (but could not explain in proper way)

Then the Panel head said that we are done with your interview and asked me to leave.

My interview lasted for around 30 – 35 minutes.

Result : Selected

I would like to wish all the best to ISRO and GATE aspirants.

I would like to thank GATEOVERFLOW specially Arjun Suresh sir, Bikram Ballav sir and all others who are working to guide computer science students.

Thank you

15
ISRO - Dreams do come true

Since 2017 , I have been reading the success stories of many ISRO aspirants of CSE from various source and always had dreamed about writing a success story. I guess the day has finally arrived. Failures have been my constant companion , but it laid the stones to my success finally. Let me give you a brief background about myself.

I am Sandeep Nithyanandan. I am 2016 B.tech graduated from Sreepathy Institute of Management and Technology , a private engineering college in Kerala . I completed my M.tech in Computational Linguistics , from GEC Palakkad in Kerala in 2019. I have been working since then in a
irm.

My Gate and ISRO exam details:
Gate 2016 - not cleared, ISRO 2016 - written not cleared

Gate 2017 - AIR 4497 , ISRO 2017 Dec - Written not cleared

Gate 2018- AIR 3039, ISRO 2018 - Written not cleared

Gate 2019 - AIR 1916, NO ISRO exam in 2019

Gate 2020 - AIR 1445 , ISRO 2020 (it is 2019 notification)- Written 108 marks and Cleared

Gate 2021- AIR 2297.

After seeing my performance you might be thinking is this guy mad. To be honest , I was never a bright student at all, my Gate score tells the same. But one thing which i did was I never gave up (being a Manchester United fan ). I kept on preparing for Gate even during my M.tech time as well as working time. Consistency really matters in the long run . I prepared every year and it helped me a lot even in the ISRO interview. The motivating factor to me was working in ISRO, that helped me a lot.

Now to the specific ISRO 2019 recruitment details:

OCT 2019 (Notification from ISRO)- 44 vaccany - This was a huge number and i was really happy. I thought this is my best chance to get selected and I have my past experience to learn from. I started preparing seriously by solving ISRO previous years and mocks as well.

May 2020- I was working and saw a notification in Gateoverflow that isro has declared the result. As usual i thought , no hope this time also. 108 till that time was my lowest in all ISRO written exams and going by ISRO written exam trend i would not qualify. I opened the result pdf with not much hope and searched my roll number. But expect the unexpected , I found the search to be showing 1/1 and i was dumbstruck to see my roll number in the selected list. The joy i had could not be explained. I was now determined to utilise the chance i got to the fullest.

May 2020- March 2021- It was one of the most uncertain period in my life. Covid came in , Work from home had started and I had to prepare for Interview. I started reading standard text books, read many interview experiences and joined many groups and prepared. But there was an uncertainty about how the interview will be done , online or offline and when will it be.

March 20, 2021 - I had chosen VSSC Trivandrum as my center. I had faced a lot of hurdles on the past day. The hotel i booked did not register my booking properly and there were issues . It made my confidence go down. But then I remembered it is all part and parcel of the game. The funny part is i forgot to wear a mask when i came out of my hotel. I felt my interview will be doomed . But somehow i managed to get one mask from outside and felt a sense of relief.

My interview was schedule on 11 am . I reached around 9.30 am. I entered into VSSC , it gave me goosebumps . I felt this is the do or die situation. When i sat in the waiting room , a lot of things flashed into my memory . 4 years of my gate preparation and a lot of other things. They called me around 12 to go to interview hall. I was waiting outside the interview hall and at 12:30pm I was called.

The next 25-30 mins was the best minutes of my life.

I am sharing the detailed interview experience below:

The interview was online this time.
I was asked to introduce myself and asked to tell my work exp , educational background and favorite subject. I introduced and told my favorite subject as OS,TOC,DS,Algo,COA. My preferred programming language was asked and i told Python and C.

I am not remembering the proper order of questions , and might have missed some questions also. Please dont mind it.I was told first TOC would be asked.

TOC

1) What is language

I was stuck for one second. But explained "A language is a subset of sigma star".

2)What is Sigma

3)Define DFA

Explained the five tuple form.

4) If NFA and Epsilon NFA exist , why go for DFA.?

I told NFA and Epsilon NFA is easier to construct than DFA. Also we have algorithm to convert NFA to DFA.

5)What is recursive language?

Expalined it using Total Turing Machine concept. I guess this was a game changer. I thank Kiran Kumar Pasupuleti sir for the teaching the TTM concept.

6)What is recursive enumerable language?

7)What is NP hard?

8)What is NP Complete?

9)What is halting problem of Turing Machine?

10)What is decidable language?

11) What is A^n B^n C^n?

I told it is CSG. But he was expecting the machine which accept it. I told its LBA.

DS

12)What is tree?

An acyclic graph which is connected.

13)What is forest?

14)How to make a stack using queue?

15)What is Binary Search tree?

16)What is AVL Tree?

I said i dont know about it.

OS)

18)Paging vs Segmentation?

19)What is Disk Scheduling algo?

I explained the FCFS, SSTF,SCAN, Elevator.

20)How can we avoid starvation.

I replied "increasing the priority of process".

Algorithm

22)Give example of Divide and Conquer, Greedy and Dynamic Programming algorithm

23)What is difference between Divide and Conquer , Dyamic Programming

25)What is inplace sorting algorithm and Not inplace sorting algorithm.

C programming

26)What is macros

27)What is inline function

COA

28)What is pipelining?

29)What are hazards

30)What is locality of reference?

31)What is write back cache?

32)What is write through cache?

CN

33)What are the layers of ISO/OSI?

34)Compare TCP and UDP?

35)In which port HTTP runs.

36)Example of UDP using Application layer protocol.

Machine Learning

37)What is Machine learning vs deep learning.

Expalined that ML need hand crafted features but DL extract features automatically. Explained some DL and ML algorithms

38)What is underfitting and overfitting.

39)What is k-crossfold validation

40)What is corelation vs covariance

(I replied i dont remember sir)

S/w Engg

41)Different stages of SDLC.

(Told me to just name them only)

42)What are different examples of testing.

43)What is regression testing

44)Good features of a s/w

They gave me hints. But I was not able to answer it

Compiler

46)Different stages of compiler.

I replied saying pre-processing, compilation. But he helped me saying that "not this. there are some stages during a compilation". I understood my blunder. I replied with all the stages.

47)What are the different examples of Code optimization.

I answered with some examples. But it was not completely correct.

DBMS

This was the last question. But since i did not prepare dbms i politely replied "I cannot recollect sir".

He said "OK . Thanks sandeep. Interview is over"

The whole interview went around 25-30 min i think.I felt it was like a rapid fire round. But in meantime they allowed me to drink some water. They tried to look at the breadth wise knowledge of my subjects. They asked questions even from outside of my favorite subject , but i answered it confidently. I guess this helped me a lot. My ML background also helped me i guess. After coming out of interview hall i felt i had given my best.

The next 5 months was very hard to pass by. The second wave came and our results were delayed.

Sept 3 2021- ISRO had given the tentative dates for the result as first week of September. Till evening 5 pm , result did not come. Around 6 , i got a telegram notification that result had come. My heart started raising and i opened the pdf. I started scrolling down from the bottom hoping that i might get at least a 44 rank. I kept on scrolling and reached the top. Then i thought i have not got selected. But then found my name on Top :)

Sandeep Nithyanandan - AIR 1 - Selected. My ISRO Dream has come true.

I literally cried after seeing this. All my years of effort has been finally approved. This was the Endgame for me and i succeeded. I would like to thank all my teachers who helped me in this journey.

I have met some very good friends.  Balaji Jegan  Mayank Raj Sajith Menon Akshay Kishore Parwateeswar Gollapalli. I would like to thank Habib Mohammad Khan Devesh Kumar Harshit Saxena Saurabh Shrivastava as they have helped and guided me a lot.

If you are determined and consistent , success will come. For me ISRO was my dream and i never gave up on it.
16
first search for how to apply for MS at IIT KGP. (it’s a complete different process)

There were different panelists with different domains, level questions keep increasing as you give the answers.

Q. What is BST?
Q. BST search complexity average and worst and when worst?

they’ll share a google doc with you to write on it as they can see it too.

Q. complexity of quicksort?
Q. write pseudo code for quicksort partition function?
Q write recursive call function of quicksort?
Q. Given this array, apply quicksort on this?
→ I totally did forget how to write partition, recursive code, even given a array I was not able to apply the quick sort on it, more because I tried to remember the quick sort solution I studied in coaching, but professors will keep supporting you, so I decided to build some new algorithm for it and developed a new algorithm for quicksort there.

Q.  How to dynamically allocate 2D array in C?
→ I don’t code in C, so told them and they were fine with it,

Q. write on the doc big Oh notation of functions.
Q. what if they f(n) and g(n) are equal.
Q. write mathematically f(n) = O g(n)
→  f(n) =< C g(n) for all n>x , need to find x given a C
Q. lots of discussion on this finding x and C?
→  not how to find it or finding them, but what to do the f(n) is equal to g(n)
→ i think i messed up here too, gave a 50-50% sure not sure answer

Interview ended.
on the same day, I received an email stating my performance was decent but for satisfying and a 2nd round of interview is being scheduled for me after 2 days. I prepared well in those 2 days, there was no sorting, searching algorithm i can’t code now, jokes apart, prepare your gate notes for DS and algo, that’s enough.

Q. Given an array find and X find pair in array whose sum is X?
→ i was happy it’s pretty standard question you would find in every preparation. they want you to start with a naive solution and then optimize it, I stated the naive solution and gave it’s complexity as n^2, and quickly wrote it’s code on the shared doc,
→ I knew the solution for O(n) but still din’t gave the answer right away
→ Then gave a optimized solution with hashmap and wrote its code which theoretically should give O(n) but was giving O(n^2) still because of searching in hashmap.keys() returns a list, I replaced it with set which again gives O(n^2) because of forming set everytime, you can use add element to set also which won’t give O(n^2), somehow we ended up to O(nLogn) as used binary search also, and i ended the discussion with the best solution i knew with O(n). believe me O(n) is the solution you’ll find in most of competitive course or website for this problem, but the professor gave me some more hints and was able to solve it in O(1), haha, shocking.

Q. asked I code for graphs, I told NO, he was happy i said NO so he can ask question on it only, Find the greatest distance can be covered in a given graph,
→ well i was not able to solve this and professor skipped it as i took lot of time.

Q. We have a problem of size N and it is divided into “b” subproblems and from those b problems we only solve “a” number of subproblems , and each problem take O(1) to solve, write recurrence relation for it.
→ never saw a question like this but as i prepared the gate notes just a day before I got the concept and solved it in seconds .

Q. In the formed recurrence relation give an example (name of algorithm) where a=b?
→ gave answer as quick sort.
Q. give an example (name of algorithm) where a!=b?
→ I had no ideas about it, after a hind i gave a right answer binary search.

Interview ended
this interview went nice. and got selected,
17
I’ll be quick,

Q. tell me about yourself ?
→ talk more about your projects, not anything else, they’ll simply ignore anything else. If you mentioned a lot of new technology in it, your interview might run on its way, for me, I kept it in the direction of what subjects I prepared.

Q. what subjects you prepared?
→ mostly DS, algo, OS, linear algebra is sufficient.

Q. What is Rank in a matrix?
→ some follow up questions on it

Q. What is BST?

Q. Explain NP problems?

DONE.

Result → selected
yup that’s it, it was simple, they really don’t want you to fail in it, they’ll stay with basic, rather too basic definitions, selections of students is very ambiguous but, the student with score 550 was also selected (gave interview much better) and student with score 650 was also rejected. Truth be told the student with a 550 score had a better understanding of subjects and concepts.
18

Research Stream Preference: Intelligent Systems (background subject: linear algebra and probability theory)

There were three professors in the panel, only two of them asked me questions. I will refer them by I1 and I2.

I1: Read out my application, mentioned my GATE score and rank, department preferences, labs selected, and asked about my BTech CGPA

He asked me why I did not apply for direct PhD and explained me benefits of doing direct PhD.

I1: What are the subjects that you have prepared for the interview?

Me: Sir, I have prepared background subjects linear algebra and probability, and familiar with subjects in GATE syllabus.

I1: I will ask you questions in probability first. Tell me if you have referred any standard book for probability?

[I mentioned the Sheldon Ross book]

I1: There are two types of random variables: discrete and continuous. Can you tell me what is the difference between the two random variables?

Me: For discrete random variables the values that the random variable (X) can take are countably finite and for continuous random variables the values are uncountable.

I1: (He was not impressed with my answer) Are you sure that is the correct statement? And is it written in Sheldon Ross book?

I1: Why do we name it continuous random variable? Why not call it uncountable random variable?

(We had discussion about this for about 5 minutes then he said that we call it 'continuous' because the cumulative distribution function for the random variable is a continuous graph.)

I1: Coming to normal random variable, can the peak of the bell curve have value greater than 1?

Me: The sum of probabilities in the range will give the total probability = 1. So total area under the curve should be 1. But I am not sure if peak could be greater than 1.

(Interviewer was not convinced with my answer. He gave me a few hints but I couldn't answer it well)

I1: What will be the value of normal random variable for $X = x$

Me: $P(X=x) = \frac{1}{\sqrt{2\pi \sigma^2}} e^{\frac{-(x-\mu)^2}{2\sigma^2}}$

I1: Right. What will be the maximum value for this? (assuming mean=0 and std=1)

Me: $\frac{1}{\sqrt{2\pi}}$ at x=0.

I1: Tell me about the binomial random variable.

Me: Told

I1: Can you say that binomial random variable is a limiting case of normal random variable? (If n is very large then will the binomial random variable become similar to normal random variable?) Prove it.

Me: I said yes but I couldn't prove the statement.

Now, the other professor took over and asked me questions on linear algebra

I2: What are eigenvalues and eigenvectors, can you define them?

Me: Sir, these are vectors whose direction remains unchanged after transformation. They might squeeze or stretch but the direction remains unchanged.

I2: Can you write the equation that you would use to calculate the eigenvalues and eigenvectors. And also explain the above definition with respect to that equation.

Me: Told

I2: Do these eigenvalues exist for every matrix mxn ?

Me: No sir, they are defined for only square matrices.

I2: Yeah, can you tell me why?

Me: In $Ax = \lambda x$ if A is rectangular matrix (m, n) and x is a (n, 1) column vector then Ax would be m-dimensional column vector (m, 1) which is different from RHS, i.e $\lambda x$ is a n-dimensional column vector (n, 1).

I2: Can you workout the above equation and show me how you will go about calculating the eigenvalues.

Me: $Ax = \lambda x$

$Ax = \lambda I x$

$(A-\lambda I)x=0$

$det(A-\lambda I)=0$

Now, we will solve for $\lambda$

I2: Okay, I understand the first two steps but why have you made $det(A-\lambda I)=0$ in the third step.

Me: Since we have $(A-\lambda I)x=0$. To solve this equation, x represents some combination of column vectors of $(A-\lambda I)$ that equate to zero. So the column vectors are not independent and hence the rank would be less than n. That would mean the determinant of (n x n) matrix should be zero if we want a non-trivial solution.

I2: Okay, now suppose I take transpose of A. Will the eigenvalues change?

Me: No sir. If $det(A-\lambda I)=0$ then $det((A-\lambda I)^T) = 0$ because the determinant remains same after transpose. Now, $det(A^T-\lambda I)=0$. Hence, the eigenvalues $\lambda$ will remain same.

I2: Okay, so you said that determinant remains unchanged after transpose. Is that true for every matrix?

Me: Yes, sir

I2: Do you know about row echelon form or reduced row echelon form. Can you name some common matrix operations?

Me: Yes sir, we can exchange two rows/columns, we can subtract/add multiple of some row/column and add to the other row/column.

I2: What would happen to the determinant if we apply these transformations.

Me: Sir, the determinant would remain unchanged.

I2: Can you take a simple matrix and show with a simple operation that determinant remains unchanged?

Me: I tried to work out a proof with a simple 2x2 matrix but couldn't clearly do it. He did give me some hint. Later I showed him an example that in a 2x2 matrix if we do $R_2=R_2-3R_1$ then the determinant value remains same.

(He was looking for a formal proof but I couldn't do it due to panic so I just showed him a simple worked out example by taking a 2x2 matrix)

The interview ended here, it lasted about 45 minutes.

My suggestion to future aspirants will be to prepare the topics from standard books right from the start of their GATE preparation. The interviewers focus on concepts and proofs which are very well explained in the standard books.

Verdict: Not Selected

19

## 7 General MCQs (5.0 marks each)

1. There is lockdown due to covid.

Ram and Gopal have decided to meet at a bus stop between 2PM to 3PM. At the bus stop a person can wait only upto 15 minutes.

If a person comes to the bus stop, he will wait for 15 minutes, or upto 3 PM, or till the other person comes up, whichever event happens earlier.

What is the probability that Ram gets covid given that Gopal is covid positive?

a. 3/4

b. 3/16

c. 1/4

d. 13/16

2. Consider 3 equations -

$x-y+2z = 1$

$2x-y+7z=2$

$-x+2y+z=b$

where 'b' is an integer. Which of the following is true?

a. The system has no solution if b=-1

b. The system has more than one solution if b=-2

c. The system has no solution if b=3

d. None of the above

3. Given a spam email detector. It detects if the email is spam or not by checking the subject line "Read this email!". If the subject line matches then the email is detected as a spam.

It is known that 4 out of 10 emails are spam.

1 percent of the spam emails have the subject line "Read this email!"

1 out of 250 non-spam emails have the subject line "Read this email!"

Find the probability that an email is spam given that spam detector marked it as spam?

a. 0.33

b. 0.625

c. 0.25

d. 0.0125

4. Given two column vectors u and v of size n each.

$W = uv^T + vu^T$

$X=u^Tv+v^Tu$

Which of the following statement is true?

a. The matrix W and matrix X are scalar.

b. The matrix W is a scalar and X is nxn.

c. The matrix W is always symmetric and nxn and X is a scalar.

d. The matrix W is nxn and X is a scalar.

5. Given a program to print the nth fibonacci number.

*A simple program to print the nth fibonacci number was given.*

What is the time complexity to find fib(n)?

a. O(n)

b. O(n^2) – This was an error in the options, it should be O(2^n)

c. O(logn)

d. O(nlogn)

6. Given $u=[a \ b \ c]^T$ and $A=\begin{bmatrix} a^2 & ab & ac \\ ab & b^2 & bc \\ ac & bc & c^2 \end{bmatrix}$is a 3x3 matrix $A=uu^T$. Given that a, b, c are all non zero real numbers. Which of the following statement is true about matrix A?

a. The matrix has three nonzero eigen values.

b. The matrix has two complex and one real eigen value.

c. The matrix has exactly two nonzero eigen values.

d. The matrix has exactly one nonzero eigen value.

7. Given a graph of a function f(x).

The graph of $f(x-1) + f(x-4)$ will be:

## 2 Programming Questions

1. Write a program to print the given matrix in clockwise spiral order. (10 marks)

2. Write a program to check if a matrix is diagonally dominant. (5 marks)

A matrix is diagonally dominant if for every row of the matrix, the magnitude of diagonal element is greater than or equal to the sum of magnitude of all non-diagonal elements of that row.

Note: The matrix contains values of type float.

20

Hello everyone.I hope you all are doing well.

Here are my GATE 2021 credentials:

Name-Akshat Kumar

GATE Paper:CS/IT

Rank-206

Score-798

Category-Non EWS General

B.E/B.Tech branch-Printing Engineering

Since I had less chances of getting CDS coursework and was anyway somewhat more inclined towards research, I decided to apply for MTech research.

Firstly,candidates where shortlisted based on their GATE scores for the written test which would be used to shortlist for interviews.Unlike 2020 where cutoff was an astonishingly high 845 GATE score for written test, this year the cut off was a generous 700.

I don’t exactly remember the questions but there were 9 MCQ questions,7 Mathematics(Linear algebra,Probability,Graphs) and 2 Programming.

7th May,2021: Written test:

1 question was on graph plotting,1 question on Baye’s theorem, 2 questions based on Eigen values, 1 question on general probability and 2 questions had all options incorrect as far as I remember. For programming, there was 1 question on spiral traversal of matrix and another was called Dominant Matrix in which we had to find number of rows in which magnitude of diagonal element  was greater than magnitude of all other elements in the row.

The test was conducted on HackerEarth Platform and was 1 hr 15 mins in duration.I attempted all questions except spiral matrix as I didn’t have much time left.

I was shortlisted for interviews after which we had to fill our lab preferences.I filled VCL AND BCL(Visual computing and Biomolecular computation labs). We also had to give Statement of Purpose for each of the labs we wanted to join.

17th May,2021:Interview:

The interview was conducted over Microsoft teams.There were 4 professors in the call.Here is my interview (Ix=interviewer x):

I1:Read out my application form details like GATE score, B.E degree and Labs preferences.

Me:Confirmed

I1:What topics have you come prepared for Akshat?

Me:Sir, linear algebra,probability,DSA and image processing basics.

I1:Starting with linear algebra.Can 2 matrices with different elements have same eigen values?

Me:(after thinking for a moment)Yes sir,

I1:Can you give me an example?

Me: Gave example by keeping major diagonal elements same and using favorable minor diagonal elements,sometimes making Minor diagonal product zero and sometimes making one of the elements as 1.

I1:That is a pretty good example.This is a property of matrix. We write it as A=PBP^(-1).

Me:Oh yes.Isn’t this condition for diagonalizable matrices, sir?

I1:Yes,good observation.Now can you prove that the two matrices A and PBP^(-1) have the same eigen values?

Me:Asked permission for using pen and paper and started thing along the equation A.X=lambda.X

After few minutes I was able to prove this and showed the solution on camera.

I1:(quite impressed)That is a really good proof. I2 now you can ask him questions.

I2:Are you comfortable with probability?

Me:Yes sir.

I2:Ok,suppose you are in a class of 30 students,what is the probability of having a birthday common with atleast 1 student in the class?

Me:Again used pen and paper.Thought in terms of discrete random variables.Say X represents number of students with whom I have a birthday in common.So basically I need to find P(X>=1) which is same as 1-P(X=0).

P(X=0)=(364/365)^29

So P(X>=1)=1-(364/365)^29.

I was also narrating my steps to I2 while solving.So I gave answer like this.

Me:Sir its a difficult calculation but would be close to 0.99.(Realized my mistake immediately and corrected)Sir actually 364/365^29 is close to 0.99 so probability would be something like 0.01 .

I2:Ok.So now suppose we have 400 students instead of 30.Would the probability increase or decrease?

Me:(A bit confused)Sir i think it would decrease.

I2:Are you sure?

Me:(Realized)No sir, actually since the number of students have increased, there is higher chance of having a common birthday and also 364/365^399 would yield a smaller value so 1-364/365^399 would have a larger value.

I2:Ok good.I3,would you like to ask some programming question(probably because my B.E was in printing XD).

I3:Yes.So can you write a program to find largest and second largest numbers in a given matrix.

Me:Yes sir.First I wrote a code finding largest in one pass and second largest in another pass and narrated the logic to I3.

I3:Ok that’s fine,can you optimize it, like try to do this in one pass.

Me:Did that.And showed the psuedo code on camera.

I3:Ok good.I4 do you have any questions?

I4:No I am fine.

I3:Ok Akshat.Your interview is over.We will now disconnect the call.

Me:Thank you sir.

My interview lasted only about 18 mins including introductions and salutations, which was relatively short,probably because I didn’t struggle much with any of the questions(not boasting).Overall, interview was great and it felt great to be interviewed by the best minds fro one of the best research universities in the world. The professors were very friendly and as far as i felt, will always guide you through if you are stuck with some question.I would definitely recommend Gilbert Strang’s MIT OCW lectures on linear algebra to be thorough with theoretical understanding of the same.First 15 lectures should suffice.

26th May,2021:The provisional shortlist was released and my application number was on the list.I was really happy but still had some fears since there is always some chance that you may not make it to the final list although such chances are less if your interview went quite well like mine.

10th June,2021:Received offer letter in mail at 7:09PM. My happiness  knew no bounds.From B.E in Printing Engineering to AIR 206 in GATE CS/IT followed by M.Tech Research at IISc CDS, what a journey this has been, I imagined as I watched my parents shed tears of happiness :’) .Thank you all. I hope I helped you somewhat and hope to see many of you at IISc next year.Cheers. :D