Avoiding cross product for accessing the matrix

Let say I have matrix A = magic(10). I want to get few selected values of A. Let say A(5,10), A(6,10), A(5,5). If for row I have vector r = [5 6 5] and c = [10 10 5], Then when I do

A(r,c), instead of three values I get 3x3. it is due to fact that for each value in r is paired with each value in c. How can I avoid this. I want that for the first value of r take first value of c and so on.

Actually I want to calculate the time for function, therefore, I have to take minimum instruction to compute.

Sorry for any inconvenience caused.

Answer 1

[Oleg Komarov]

pos = sub2ind(size(A), r,c)
A(pos)

[Junaid]

Thank you Oleg, It is really two line of code which really helped me.

Could you please do me an other favor. Let say A is the matrix of size 100 x 100, A is kind of lookup table.

and There is an other matrix B that has the size let say 10 x 100. Where each col is histogram. Now for Query col vector Q size of 10 x 1.

I want to get resultant matrix R of size(B), where each cell value in R, is obtained by looking the values of Q and B in A.

let say:

R(1,1) = A( Q(1), B(1,1));

R(5,5) = A(Q(5)), B(5,5));

I hope you understand the scenario.

Thanks a lot in advance.

[Daniel Shub]

You should ask this as another question.

[Andrei Bobrov]

Hi Oleg! Finally then, you're back!