Making a matrix act like a coordinate plane

I have two square matrices and want all the cells to reflect their quadrant in the matrix

for x for y

-+ ++

-+ - -

The matrices are 100x100 and the axes are row/columns 50 and 50. All values are default 0 or positive.

m(1:50,:) = -m(1:50,:); %This only makes the top quads negative in both matrices.

Thanks!

Answer 1

[KSSV]

x = -50:50 ; 
y = -50:50 ; 
[X,Y] = meshgrid(x,y) ; 

[Sean Spencer]

I still had to invert the Y but thank you for the help!