How can I format the output of a for loop as a matrix so I can apply surf?

I need to create a piecewise function that I can graph using surf. The function is:

 for 0<x<12pi and 0<y<12pi,
Z = sin(x) + sin(y) - 1  if z>0
    0                    if z<0
%not code

A for loop seems like an easy way to do this. I used:

 [X,Y] = meshgrid(0:.2:(12*pi), 0:.2:(12*pi)); %defining my domain
Z = sin(X)+sin(Y)-1; 
for i=X
    for j=Y
        if Z > 0 
           Z = Z;
        else
        Z = 0;
        end
    end
end    
figure
surf(X,Y,Z)

which produces the errors:

Error using surf (line 57) Z must be a matrix, not a scalar or vector.

Error in model1 (line 13) surf(X,Y,Z)

(model1 is the name of my script)

Any advice? Simplicity appreciated.

Answer 1

[Star Strider]

Use an anonymous function for ‘Z’ (I created the function as ‘ZF’, and the variable as ‘Z’).

The loop is not necessary:

[X,Y] = meshgrid(0:.2:(12*pi), 0:.2:(12*pi)); %defining my domain
ZF = @(X,Y) sin(X)+sin(Y)-1;
Z = ZF(X,Y);

figure(1)
surf(X,Y,Z)
grid on

[Tony Theis]

Thanks for the response, but maybe my intentions weren't clear. I essentially want to define a maximum function where (to use your notation):

Z=ZF when ZF >0, and

Z= 0 when ZF <0,

and then graph Z using surf (or any other 3D graphing command) to produce a surface on the xy plane, with mounds made by the tips of the sine waves.

[Star Strider]

Missed that, sorry.

I believe this now does what you want:

[X,Y] = meshgrid(0:.2:(12*pi), 0:.2:(12*pi)); %defining my domain
ZF = @(X,Y) sin(X)+sin(Y)-1;
Z = ZF(X,Y).*(ZF(X,Y) > 0);

figure(1)
surf(X,Y,Z)
grid on