How to convert circumferential data to angular data in Matlab?

I have a Matrix H which is the addition of two matrix G,FF .Both G and FF must be defined with circumferential data i.e.

x =linspace(0,2*pi*r,ntn); 
y=linspace(x_2,x_1,nz);
[X,Y]=meshgrid(x,y);
H = G + FF;

Finally I want to show the variation of H and proceed the calculation with theta co-ordinate and dimensionless Y co-ordinate. I defined two more linspace (0,2*pi,ntn) and (0,1,nz) and plotted H. But the results are found to be incorrect because of unequal grid size.

Kindly help me in this regard.

Thanks.