function [x, y, z] = ellipsoid(xc, yc, zc, xr, yr, zr, N);
Inputs:
xc,yc,zc - the coordinates of the center of the file
xr,yr,zr - the dimensions of the ellipsoid
N - number of points
Outputs
x,y,z - are N+1xN+1 matrices suitable for plotting using the surf function
surf(x,y,z)