It's more than two months from the last time I opened any books and read after the gate. Please don't laugh when you feel why I didn't answer even some simple questions ?.
My IISc Intelligence systems RA interview was scheduled on the 23rd afternoon.
Written test: The questions are very clear, from basic concepts of linear algebra, probability, one question on heaps, one question on pointers, likewise.
Interview shortlisted candidates were declared nearly after 30 min when written was over.
Around 10 people were shortlisted.
I was second from last.
When it's my turn,
Me: entered the room.
Panel: 3 male professors, very old (I can say the very experts in their areas), one professor for probability(PP), one professor for linear algebra(PLA), other professor was busy in working with laptop whole the time of the interview.
PLA: With a bunch of documents in hand, read all my academic details, gate score, areas I chose for RA, to make me feel comfortable.
PLA: What topics we start with in LA?
me: eigenvalues and eigen vectors, linear system of equations…
PLA: dictated two v,u 4*1 column vectors. v = [ 1 2 3 4] , u = [ 5 6 7 8 ] ( please imagine them as column vectors though I wrote them as row vectors)
A = v* u'. What is the order of A?
Me: after doing rough work on board to show how I got it, told " 4*4 sir"
PLA : Good. Write down A.
PLA: what are the eigen values of A?
Me : wrote characteristic equation and told the roots of this equation are our required eigen values.
PLA: How Did you get that equation?(He is asking for proof)
Me: $Ax = \lambda x$
$Ax – \lambda x$ = 0
$(A - \lambda I ) x = 0$
Since x is non zero vector, $|A - \lambda I |= 0$
PLA: what if you put (0,0,0...0) in x? does the equation satisfy?
me: yes, sir.
PLA: won’t it make (0,0,..0) as one of eigen vectors? (to confuse)
me: yes, sir, but it’s a kind of trivial solution ( I am dead here)
PLA : Since you are saying all 0’s to be an eigen vector, that means can I put any value of lambda in that equation?
me: Realized my mistake, but unable to think of a proper explanation for why the ‘x’ is treated non zero in the definition of eigen values I remained silent and acted like I am thinking about how this whole universe began at the first place.
PLA: anyway, tell me the eigen values of A
me: triying to solve, interrupted
PLA: can’t you tell at least one eigen value by looking at the nature of matrix A without solving?
me: Acted like I am thinking about “did aliens ever visit earth”? while looking at the matrix, *Silence
PP: Breaking the silence, shall we move on to probability?
me: yes, sir.
PP: which textbook you referred to while preparing?
me: +2 sir. (I really didn’t spend time to prepare, so in last minute I just read my +2 book, to brush up my basics before interview)
PP: Tell me an example of Random Variable.
me: Counting the no.of heads when two coins are tossed.
PP: good. What is that random variable called?
me: Bernoulli Random variable, sir.
PP: with a smile, it’s binomial, not Bernoulli.
me: smiled and said “ sorry, sir. yes it is binomial” ( I know it but in that interview fear, I answered it like that, and the professor completely understood that)
PP: Write the PDF for binomial distribution.
me: wrote P(X=x) = nCx. pow(p, x) . pow(q,n-x).
PP: good. explain each and every variable in it.
PP: what are all the values x can take?
me: real values
PP: that means can I put 2.55 or something?
me: realizing the mistake, said 0 to n sir.
PP: good. why are you doing p*p*p*...x times in that function?
me: since ‘n’ trails are independent of each other and ‘p’ is success probability and we want ‘x’ no of successes, we are getting pow(p,x)
PP: what are independent events? Depending on what you are given freedom to multiply p*p*p….(same question is repeated till the end of the interview like more than 6 times cause professor didn’t satisfy)
me: all the different explanations I gave are
“occurence of one event doesn’t effect another”
“P(A intersection B ) = P(A) P(B)”
“P(A|B) = P(A) if A and B are independent”
“P(A|B) = P(A intersection B)/P(B) and to be independent then P(A intersection B) = P(A).P(B)”
PP: what if P(B) = 0 ( pointing to the last point I wrote on board)
me: In the definition of conditional probability it’s explicitly mentioned that P(B) != 0.
PP: yes, but then there should be some universal definition of independent events, right? Excluding all such exceptions!
me: Again acted like I am thinking about the creation and existence of black holes. * Silence……...
PP: “ see, this is a very serious program, you should prepare a lot in these areas and come”
me: At this point, after listening to those words, “ I felt bad, felt shameful to waste their time and unable to reach their expectations”. ( But I am able to smile throughout the interview and made them think I am taking everything positively, of course, I took +vely.).
me: Leaving the room, “Sir, may I know the answer for that independent events”?
PP: I will tell you, wait outside.
But, since I am getting late to catch a train, I left the campus.
For 2020 aspirants,
Post gate preparation is very powerful, cause those who got risky ranks can have the chance to outperform the toppers in interviews and written tests. Facing interviews and getting selected should be a true aspirant motto. Here, one point I like to mention is, I have the chance to get direct admits in IITs and even got one in round 1. But, it would be great if you dedicate your time, even after the gate to attend interviews and written tests though you are AIR 1.
This is my interview experience and conclusions I made to myself. I thought this will help others out there. Thank you.