Deleting a row or column of a matrix

I have a Matrix but I only need the first 20 columns of the matrix. I was wondering if there was a way to delete the rest of the matrix instead of having to create a new matrix all together. If it's not possible is there a better way of doing this compare to

for j=1:20
      for k=1:20
                  u(j,k)=y(j,k)
      end
end

Thanks in advance!

Answer 1

[Fangjun Jiang]

Or y(21:end,21:end)=[]

[Sean de Wolski]

Glass half empty; but you win!

Answer 2

[Sean de Wolski]

u = y(1:20,1:20);

[Fangjun Jiang]

My condolences... :)