A = [16 3 2 13; 5 10 11 8; 9 6 7 12; 4 15 14 1]

Matlab has a preference for working with the columns of a matrix.

To work with rows, transpose a matrix, see below

switch an array as if flipping it upon both axis

A'                    - tranpsoses numbers and changes sign of any complex elements
A'.                   - transposes numbers w/o changing sign
sum(A')'              - sum rows into a column vector
diag(A)               - main diagonal elements of an array
sum(diag(A))          - sum of the main diagonal elements of an array
fliplr(A)             - flips the array from left to right
sum(diag(fliplr(A)))  - sum of the antidiagonal

A(row, col)  - refers to specific element in array
A(4,2) = A(8)

A(4,5) = 17  - granted that the 5th column doesn't exist, it is added, with the number