How to use surf to plot sphere function in matlab

I'm trying to plot sphere function below, But I'm getting wrong result

Here is the code I'm using

    x1 = [-10:1:10];
    x2 = [-10:1:10];
    y = zeros(1,21);

    for i = 1:21
        y(i) = sphere([x1(i) x2(i)]);
    end
    Y = meshgrid(y);
    surf(x1,x2,Y);
    colormap hsv;

`sphere.m`

    function [y] = sphere(x)
    d = length(x);
    sum = 0;
    for i = 1:d
      sum = sum + x(i)^2;
    end
    y = sum;
    end

[Walter Roberson]

You can replace that code for sphere with

sphere = @(x) sum(x.^2);

[Walter Roberson]

This question appears to duplicate http://www.mathworks.com/matlabcentral/answers/301883-code-for-plotting-sphere-function . Please explain the difference between the questions, other than the fact that you posted code here.

Answer 1

[KSSV]

Have a look on:

http://in.mathworks.com/matlabcentral/fileexchange/34143-meshing-thin-shells-using-four-noded-elements/content/Shell%20Mesh/SphericalShell.m