%
% Written by:
% --
% John L. Weatherwax                2009-04-21
%
% email: wax@alum.mit.edu
%
% Please send comments and especially bug reports to the
% above email address.
%
%-----

close all; clc; clear;

% EPage 137

x = -4:0.2:+4;
y = -4:0.2:+4;

[X,Y] = meshgrid(x,y);

Z = 0.5 * ( X.^4 - 16 * X.^2 + 5 * X ) + 0.5 * ( Y.^4 - 16 * Y.^2 + 5 * Y );

x_star = -2.9035;
z_linear_interp = interp2( X, Y, Z, [x_star], [x_star], 'linear' )

z_cubic_interp = interp2( X, Y, Z, [x_star], [x_star], 'cubic' )

z_exact = 0.5 * ( x_star^4 - 16 * x_star^2 + 5 * x_star ) + 0.5 * ( x_star^4 - 16 * x_star^2 + 5 * x_star )