Index Vector Operation in Matlab

If the matrix A and the vector b

A = 5×5

13 2 3 3 10

14 5 15 7 1

2 9 15 14 13

14 15 8 12 15

10 15 13 15 11

b=[1 2 3 4 5]

and

>> C=A(b)

ans =

13 14 2 14 10

How to get element C by index in vector A(b) ?

[KALYAN ACHARJYA]

What does it mean?

ans =
     3    12     5     8     3

Is this expected ans?

[James Tursa]

It is unclear what you are trying to do, given that your code above does not produce the answer you post. E.g.,

>> A = [    13     2     3     3    10
    14     5    15     7     1
     2     9    15    14    13
    14    15     8    12    15
    10    15    13    15    11];
>> b=[1 2 3 4 5];
>> C = A(b)
C =
    13    14     2    14    10

Can you provide more explanation?

[Johan Johan]

I corrected the mistake.

[James Tursa]

Please restate your question. What do you mean by "get element C by index in vector A(b)"? Are you trying to do something like A(b)(2) to get at the 2nd element of C directly? If so, you cannot use that syntax in MATLAB.

Answer 1

[Jon]

Actually A(b) with the example you have given will return [13 14 2 14 10]. That is the elements are taken from the first column of A. Note that using linear indexing (indexing a two dimension array with a vector of indices, rather the pairs of indices) will provide the elements columnwise.

I'm not clear whether this is what you are asking. What do you mean by get element C by index in vector A(b) ?