Matrix manipulation

Question 1

Define matrix A
| 1 2 |
| 3 4 |
| 5 6 |

Answer 1

A = [1 2; 3 4; 5 6]

Question 2

Identity matrix of size 3

Answer 2

eye(3)

Question 3

"Vectorize" elements of a matrix A:
| 1 2 |
| 3 4 |
to
|1|
|2|
|3|
|4|

Answer 3

A(:)

Question 4

Transpose matrix A

Answer 4

A’

Question 5

Exact inverse of a square martix A

Answer 5

inv(A)

Question 6

Generalized inverse of matrix A. Properties?

Answer 6

pinv(A)

A may be square or non square or singular. Pseudo-inverse solves for best fit of a solution to inverse problem.

Question 7

Element ‘3’ of matrix A:
| 1 2 |
| 3 4 |
| 5 6 |

Answer 7

A(2,1)

Question 8

Element ‘6’ of matrix A:
| 1 2 |
| 3 4 |
| 5 6 |

Answer 8

A(3,2)

Question 9

First column of matrix A:
| 1 2 |
| 3 4 |
| 5 6 |

Answer 9

A(:,1)

Question 10

Second row of matrix A:
| 1 2 |
| 3 4 |
| 5 6 |

Answer 10

A(2,:)

Question 11

First and third row of matrix A:
| 1 2 |
| 3 4 |
| 5 6 |

Answer 11

A( [1 3], : )

Question 12

Copy 3rd row to 1st row of matrix A:
| 1 2 |
| 3 4 |
| 5 6 |

Answer 12

A( 1, : ) = A ( 3, : )

Question 13

Retrieve number of rows of matrix A.

Answer 13

size(A, 1)

Question 14

Retrieve number of columns of matrix A.

Answer 14

size(A, 2)

Question 15

Retrieve greater dimension of matrix A.

Answer 15

length(A)

Question 16

Retrieve indices of vector v that are greater than 3.

Answer 16

find(v > 3)

Question 17

Map matrix A to a matrix of same dimensions but with elements equal to 0 or 1 when A(i,j) is 3 appropriately.

Answer 17

A > 3