How to draw a 3D graph with constraints?

I want to draw a 3D graph for a function with several contraints.

For example, f(x,y)=1-0.5*x-0.7*y such that 0<=x<=1, 0<=y<=1, 0<=x+y<=1.

Since I am a beginner of using MATLAB, so any help would be very appreciated.

Answer 1

[John D'Errico]

The simple answer is to just use meshgrid.

[x,y] = meshgrid(linspace(0,1,100));

keepind = (x + y) <= 1;
x(keepind) = NaN;
y(keepind) = NaN;
f = 1 - .5*x - .7*y;

surf(x,y,f)

[DL]

Thank you so much, John!! It works great!

[DL]

One more question.

When the graph, f(x,y) is drawn, I would like to have a different color gradation for the region f(x,y)>=0 vs. f(x,y)<0.

For example, for the region f(x,y)>=0 is a blue-color gradation, but a red one for the region where f(x,y)<0.

Can you kindly help me out?

Thank you.

[Xiaohu Wu]

A great example!

[Vikas Sharma]

Isn't it should x(~keepind)=NaN and y(~keepind)= NaN