MATLAB: I am having matrix of i rows by 3 columns ,now i want to multiple only i rows of 1 columns with 5 upto 100th row after the 100th row ,values has to be as it is.

Question

i= 3560 A = (i,3)

now want to multiple A(i,1) with some value say 5 but upto say 100 and then remaining values of rows has to be same.

and want to save New A(i,1) (change) with 1 to 100 i.e multiplied with 5 and remaining unchanged values in New A(i,1)

Answer 1

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)