How do i write the function for 3D graph which include summation?

I would like to create a 3D graph for function z, where z takes the form of:

z=3x+2y+sum(k[i]*sqrt((y-a[i])^2+(x-b[i])^2)

Suppose i=1:3,

the values for k[i],a[i],b[i] are known.

I have defined

k=[c1 c2 c3];
a=[c4 c5 c6];
b=[c7 c8 c9];

where c is constant.

The function i can think of is:

z=3*x+2*y+sum(k.*sqrt((y-a).^2+(x-b).^2)

but it seems to be wrong as i keep getting the error message of "Matrix dimensions must agree."

What would be the correct way for constructing above function?

Answer 1

[Walter Roberson]

 [x, y] = ndgrid( xvalues, yvalues );

 z = 3 * x(:) + 2 * y(:) + sqrt( bsxfun(@minus, y(:), a).^2 + bsxfun(@minus, x(:), b).^2 ) * k;

Reshape to size(x) if you want.

Note that the "* k" is intended as matrix multiplication, and thus implicitly includes doing the summation.