plot a conditional equation

I want to plot f(x,y)= (x-y)/(x+y) with this condition that x,y> 0 and y>10x, how can I plot it in matlab?

Answer 1

[Walter Roberson]

syms x y
f(x,y) = piecewise(y > 10*x, (x-y)/(x+y), nan)

f(x, y) = 

fsurf(f, [0 1000 0 1000])