Define 
, 
, x = [x1;x2];
The x here is a matrix of 2 by n: 
z = x.' * x;
Here z is matrix multiplication of 
(x.') and x.
(x.') and x. 
The result z is an nxn matrix. But it does not mean that z = x1^2 + x2^2.
When you define x1 and x2 as follows:
[X1,X2] = meshgrid(x1,x2)
,
z = X1.^2 + X2.^2
Then X1.^2 is the element-by-element square, so that
