Plot surface data which satisfies x/y condition

Hello,

I have a function g(x,y). I want to plot the surf data only for areas where condition x + y = 5 is satisfied. How can I do this?

My code so far:

g = matlabFunction(f1);
[x y]=meshgrid(brk,brk);
data = g(x,y);
figure(1)
surf(x,y,data)

Answer 1

[KSSV]

x = -10:1:10 ; 
y =  -10:1:10 ;
[X,Y] = meshgrid(x,y) ; 
idx = X+Y==5 ;  
Z = double(idx) ; 
surf(X,Y,Z)
shading interp
colorbar