Question 863275
If a and b have the same dimensions, then the sum of the matrices is the matrix where each ij-th element is the sum of the ij-th elements of a and b.
If a and b don't have the same dimensions, then the sum is not defined.
Example:
{{{(matrix(2,2,1,0,0,1))+(matrix(2,2,5,6,1,-1))=(matrix(2,2,1+5,0+6,0+1,1-1))=(matrix(2,2,6,6,1,0))}}}