# Recent questions tagged matrices 1
Suppose that $P$ is a $4 \times 5$ matrix such that every solution of the equation $\text{Px=0}$ is a scalar multiple of $\begin{bmatrix} 2 & 5 & 4 &3 & 1 \end{bmatrix}^T$. The rank of $P$ is __________
2
Consider the following matrix.$\begin{pmatrix} 0 & 1 & 1 & 1\\ 1& 0& 1 & 1\\ 1& 1 & 0 & 1 \\1 & 1 & 1 & 0 \end{pmatrix}$The largest eigenvalue of the above matrix is __________.
1 vote
3
If $P$ is an invertible matrix and $A=PBP^{-1},$ then which of the following statements are necessarily true? $B=P^{-1}AP$ $|A|=|B|$ $A$ is invertible if and only if $B$ is invertible $B^T=A^T$
4
Let $A=\begin{bmatrix} 1 & 2 & 3 \\ 4 & 5 & 6 \\ 7 & 8 & 9 \end{bmatrix}, B=\begin{bmatrix} 1 & 4 & 7 \\ 2 & 5 & 8 \\ 3 & 6 & 9 \end{bmatrix}, C=\begin{bmatrix} 4 & 5 & 6 \\ 1 & 2 & 3 \\ 7 & 8 & 9 \end{bmatrix}$ and $D=\begin{bmatrix} -1 & 2 & 3 \\ 4 & -5 & 6 \\ 7 & 8 & -9 \end{bmatrix}$. Which of the following statements are true? $|A|=|B|$ $|C|=|D|$ $|B|=-|C|$ $|A|=-|D|$
5
Let $x=\begin{bmatrix} 3& 1 & 2 \end{bmatrix}$. Which of the following statements are true? $x^Tx$ is a $3\times 3$ matrix $xx^T$ is a $3\times 3$ matrix $xx^T$ is a $1\times 1$ matrix $xx^T=x^Tx$
6
A $n\times n$ matrix $A$ is said to be $symmetric$ if $A^T=A$. Suppose $A$ is an arbitrary $2\times 2$ matrix. Then which of the following matrices are symmetric (here $0$ denotes the $2\times 2$ matrix consisting of zeros): $A^TA$ $\begin{bmatrix} 0&A^T \\ A & 0 \end{bmatrix}$ $AA^T$ $\begin{bmatrix} A & 0 \\ 0 & A^T \end{bmatrix}$
7
For numerical answers, the following forms are acceptable: fractions, decimals, symbolic e.g.:$\left( \begin{array}{c} n \\ r \end{array} \right)^n P_r , n!$ etc. Suppose $A,B$ and $C$ are $m\times m$ matrices. What does the following algorithm compute? (Here $A(i,j)$ denotes the $(i.j)^{th}$ entry of matrix $A$.) for i=1 to m for j=1 to m for k=1 to m C(i,j)=A(i,k)*B(k,j)+C(i,j) end end end
8
For numerical answers, the following forms are acceptable: fractions, decimals, symbolic e.g.:$\left( \begin{array}{c} n \\ r \end{array} \right)^n P_r , n!$ etc. In computing, a floating point operation (flop) is any one of the following operations performed by a computer ... $c_{ij}=\displaystyle\sum^5 _{k=1} a_{ik} b_{kj}$. How does this number change if both the matrices are upper triangular?
9
$\text{Description for the following question:}$ A golf club has $m$ members with serial numbers $1,2,\dots ,m$. If members with serial numbers $i$ and $j$ are friends, then $A(i,j)=A(j,i)=1,$ otherwise $A(i,j)=A(j,i)=0.$ By convention, $A(i,i)=0$, i ... $A^4(1,3)=0$. Then which of the following are necessarily true? Give reasons. Member $1$ and member $2$ have at least one friend in common.
10
$\text{Description for the following question:}$ A golf club has $m$ members with serial numbers $1,2,\dots ,m$. If members with serial numbers $i$ and $j$ are friends, then $A(i,j)=A(j,i)=1,$ otherwise $A(i,j)=A(j,i)=0.$ By convention, $A(i,i)=0$, i.e. a person ... $A^2(i,i)>0$ for all $i,\;1\underline< i \underline < m.$
11
$\text{Description for the following question:}$ A golf club has $m$ members with serial numbers $1,2,\dots ,m$. If members with serial numbers $i$ and $j$ are friends, then $A(i,j)=A(j,i)=1,$ otherwise $A(i,j)=A(j,i)=0.$ By convention, $A(i,i)=0$, i.e. a person ... $A^4(1,3)=0$. Then which of the following are necessarily true? Give reasons. $m\underline < 9$
$\text{Description for the following question:}$ A golf club has $m$ members with serial numbers $1,2,\dots ,m$. If members with serial numbers $i$ and $j$ are friends, then $A(i,j)=A(j,i)=1,$ otherwise $A(i,j)=A(j,i)=0.$ By convention, $A(i,i)=0$, i.e. a person ... $A^4(1,3)=0$. Then which of the following are necessarily true? Give reasons. $m\underline> 6$
Consider the matrix $A=\begin{pmatrix} 0 & -1 \\ 1 & 0 \end{pmatrix}$. Find $A^n,$ in terms of $n,$ for $n\geq2.$
For a matrix $M=[m_{ij}]; \: i,j=1,2,3,4$, the diagonal elements are all zero and $m_{ij}=-m_{ji}$. The minimum number of elements required to fully specify the matrix is ________ $0$ $6$ $12$ $16$