Why can't I generate a 3-d surface when using surf? (file)

My version is 2015b. I use Mac.

x=linspace(-2,2,20);

y=x';

z=y*x;

surf(x,y,z)

And the output has nothing, shownd in picture.

Answer 1

[Cris LaPierre]

Z must be a matrix. In your code, it is only a vector. Follow the eamples on the surf documentation page. You will find meshgrid helpful for this purpose.

x=linspace(-2,2,20);
y=x';
[X,Y] = meshgrid(x,y);
Z = X.*Y;
surf(x,y,Z)

[John D'Errico]

Actally, in the code shown by @WEN SHIN LU, z is a matrix, because it was created as an outer product of the vectors y*x, where y is a column vector, and x a row vector. So the code shown does work.

x=linspace(-2,2,20);
y=x';
z=y*x;
surf(x,y,z)

[Cris LaPierre]

Good point. I wonder what the issue is then.

[WEN SHIN LU]

Thank you! I found it's about my files. I created a file called surf before. That's the issue.