How to assign the values to a matrix?

Dear All,

I have a zero matrix A whcih needs to be assigned values from an column vector B. The indecies of those elements are stored in a two-columns array C.

For example, B = [1 9 12 31], C = [1 4;3 6;5 2;6 3]. Then matrix A is =[0 0 0 1 0 0; 0 0 0 0 0 0; 0 0 0 0 0 9;0 0 0 0 0 0; 0 12 0 0 0 0;0 0 31 0 0 0].

Thanks a lot.

Benson

Answer 1

[Stephen23]

https://www.mathworks.com/help/matlab/ref/sub2ind.html

B = [1,9,12,31];
C = [1,4;3,6;5,2;6,3]

C = 4×2

1 4 3 6 5 2 6 3

A = zeros(6,6);
% assign those values:
X = sub2ind(size(A),C(:,1),C(:,2));
A(X) = B

A = 6×6

0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 12 0 0 0 0 0 0 31 0 0 0

For comparison:

[0 0 0 1 0 0; 0 0 0 0 0 0; 0 0 0 0 0 9;0 0 0 0 0 0; 0 12 0 0 0 0;0 0 31 0 0 0]

ans = 6×6

0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 12 0 0 0 0 0 0 31 0 0 0