Let's assume that you want to multiply the first 'x' rows of the first column with a scalar 'n' and update the values in 'A'.
You can use the following command to do this:
>> A(1:x,1) = n*A(1:x,1);
If you want to do this for multiple columns (say first y columns) at once, you can do similar operation by indexing into columns also:
>> A(1:x,1:y) = n*A(1:x,1:y)
