Add a value to an element in a matrix

Hi,

Given the following matix

D=[1 2 3 4 5 6 7 8] 
A(1:length(D),1:10) = 110 
S= [0 0 8 0 0 8 0 0; 0 0 0 5 0 0 0 0];

I want to add the value different from 0 in S, to a specif location in A.

A =

   110   110   110   110   110   110   110   110   110   110
   110   110   110   110   110   110   110   110   110   110
   110   110   110   110   110   110   110   110   110   110
   110   110   110   110   110   110   110   110   110   110
   110   110   110   110   110   110   110   110   110   110
   110   110   110   110   110   110   110   110   110   110
   110   110   110   110   110   110   110   110   110   110
   110   110   110   110   110   110   110   110   110   110

In particular, the value 8 must be added in the 6th column of A, while the value 5 must be added to the second column of A.

To understand in which raw to allocate the element, it depend on the position in S.

1) In this case the first 8 is in position (1,3) so must be allocated in A(3,6): 3 because it's in position 3 and 6 because all the values different from zero of the first raw of S must be added in the 6th column of A

2) The second 8 is in position (1,6) so must be allocated in A(6,6)

3) The first 5 is in position S(2,4) so must be allocated in A(4,2): 4 because it's in position 4 and 2 because all the values different from zero of the 2 raw of S must be added in the 2th column of A

Finally i want to obtain

A =

   110   110   110   110   110   110   110   110   110   110
   110   110   110   110   110   110   110   110   110   110
   110   110   110   110   110   118   110   110   110   110
   110   115   110   110   110   110   110   110   110   110
   110   110   110   110   110   110   110   110   110   110
   110   110   110   110   110   110   110   110   110   110
   110   110   110   110   110   118   110   110   110   110
   110   110   110   110   110   110   110   110   110   110
  
   

[Guillaume]

Why do the non-zero values is S(:, 1) go to column 6 and those in S(:, 2) go to column 2? There doesn't seem to be any logic to that. Which column would non-zeros in the 3rd row of S end up in?

[luca]

Cause is a specific problem where I need to add that values of S just in these columns of A

Answer 1

[Guillaume]

Cause is a specific problem where I need to add that values of S just in these columns of A

Then, this should work:

A(S(1, :) ~= 0, 6) = nonzeros(S(1, :));
A(S(2, :) ~= 0, 2) = nonzeros(S(2, :));

Of course, if there were more rows in S a completely different approach would be better, but for just 2 rows this will do.

[luca]

S has two raws but could have more columns in the real case. So it's ok.

But with your solution you are substituting the value in A with the one in S. What I want is to sum the value of S to the one of A

[luca]

A(S(1, :) ~= 0, 6) = A(S(1, :) ~= 0, 6) + nonzeros(S(1, :));
A(S(2, :) ~= 0, 2) = A(S(2, :) ~= 0, 2) +  nonzeros(S(2, :));

is it ok?

[Guillaume]

Yes, it is ok. But why didn't you try?

[luca]

I tried. I've just reported in case someone else is interested in the topic.

Thanks Guillaume