How to plot a triangular shape function on a triangular domain?

Hello, I want to plot the following shape function: N(s,t)=t*(2*t-1) It has to look like the following diagramm:

but I get this one:

Here is my code:

[s,t]=meshgrid(0:0.1:1,0:0.1:1)
N3=@(s,t)t.*(2*t-1);
surf(s,t,N3(s,t))

I know that the problem is with the rectangular domain, that meshgrid generates. But I don't know how to define a triangular domain. Has anybody an idea?

Thanks

Answer 1

[Mike Garrity]

I described one approach in this thread.

[Soroush Asarzadeh]

Hi Mike, Thank you for your quick answer. Unfortunately I can't apply it to my case. In your approach you have used: out = w<0; which is not going to work in my case. Can you please make it more clear by helping me to define the exclusion area?

When I even manage to do that, I'll have NaN elements in my N3-matrix, which causes the following error:

Subscript indices must either be real positive integers or logicals.

any idea about this?

Thanks

[Mike Garrity]

I think that passing a function handle into surf is making things more complicated than you really need.

I don't know what N3 is, but using the N from the top, I get this:

[s,t] = meshgrid(0:0.025:1);
z = t.*(2*t-1);
z(s+t > 1) = nan;
surf(s,t,z)

[Soroush Asarzadeh]

Thank you very much Mike!