MATLAB: How to change a specific group of diagonal values within a matrix, but still print the whole matrix

MATLABmatrix manipulation

I have 44×22 matrix [T] and I want to apply an equation to a specifc group of cells within the matrix, which are on a diagonal with each other.
0 0 1 0 0 0 . . .
0 0 0 1 0 0 . . .
0 0 0 0 1 0 . . .
0 0 0 0 0 1 . . .
Here the 1's are an example of potential cells that I'd like to change. I know that by using the "diag" function I could change those values, but I haven't found a way to keep those changed values stored within the matrix.

Best Answer

Check this example. Suppose you have a 4x4 matrix
x = [1 2 3 4; 5 6 7 8; 9 10 11 12; 13 14 15 16];
>> x
x =
     1     2     3     4
     5     6     7     8
     9    10    11    12
    13    14    15    16
and you want to change this diagnal
diag([1 1 1],1)
>> diag([1 1 1],1)
ans =
     0     1     0     0
     0     0     1     0
     0     0     0     1
     0     0     0     0
You can do it like this
x = [1 2 3 4; 5 6 7 8; 9 10 11 12; 13 14 15 16];
mask = diag([1 1 1],1)==1;
x(mask) = 2*x(mask); % multiply the element on that diagonal by 2
Result:
>> x
x =
     1     4     3     4
     5     6    14     8
     9    10    11    24
    13    14    15    16
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