There are several issues you need to resolve with your code before it will run. First, there is no increment operator in MATLAB, so expressions like
need to be replaced with
Once you make those changes, you'll get an error about indexing... something like
Attempted to access TRI(6,0,2); index must be a positive integer or logical.
This is because the matrix A has zeros as entries, and you're using the entries of A to index into TRI. Since I don't know your end goal, I can't suggest with much certainty how to fix that error, but the code below will run. I've added comments to every line i changed. See if it produces what you're looking for and if not, respond with the issue...
A = A + 1;
TRI(A(k,m),A(k,m+1),k) = TRI(A(k,m),A(k,m+1),k) + 1;
k = k+1;