clear
clc
[ x1, x2 ] = meshgrid( -1 : 0.005: 1 );
Ras = 20 + x1 .^ 2 + x2 .^ 2 - 10 * ( cos( 2 * pi * x1 ) + cos( 2 * pi * x2 ) );

% subplot( 1, 2, 1 )
% surf( x1, x2, Ras )
%
% subplot( 1, 2, 2 )
contour( x1, x2, Ras, 20 )
set( gca, 'xlim',[ -1, 1 ], 'ylim', [ -1, 1 ] )