ERROR: Z must be a matrix, not a scalar or vector.

What's the problem with the following code?

syms x y;

f=input('enter function: ','s');

f = symfun(eval(f), [x y]);

[X,Y]=meshgrid(-10:1:10);

mesh(f);

when i run the above code after entering a function the following error occurs:

Z must be a matrix, not a scalar or vector.

Answer 1

[Star Strider]

There is no reason to use the Symbolic Math Toolbox here. Core MATLAB fiunctions will work.

The Code —

f=input('enter function: ','s')
% f = 'x.^2 + sin(y)';                            % Test Function
f = str2func(['@(x,y)' f]);
[X,Y]=meshgrid(-10:1:10);

mesh(X,Y,f(X,Y));

[geometry geometry]

Thank you...

but one question:

when I enter the function log(x^2+y^2) an empty figure appears; what's the problem with this?

and when I enter log(x) the following error occurs:

X, Y, Z, and C cannot be complex.

[Star Strider]

My pleasure.

You need to be certain that ‘f’ does element-wise operations. Change the str2func call to include a vectorize call:

f = str2func(['@(x,y)' vectorize(f)]);

See the documentation on the various functions to understand how they work, and the documentation on Array vs. Matrix Operations (link) to understand the reason the differences are important.