Help with drawing contour lines for a certain 3D surface

Hello guys, I would appreciate if anyone can help me to draw contour lines for a certain function on a 3D drawing? My matlab code is:

load C1.txt % The Nodes coordinates Matrix load EC.txt % Element Connectivity Matrix load CC1.txt % Element stress colors

Nd=max(C1(:,1)); % No of Nodes Nodes=zeros(Nd,3); Nodes(C1(:,1),:)=C1(:,2:4); % Coordinates of the Nodes including the unintialized nodes NE=size(EC,1); % No of Elements

X=[Nodes(EC(:,1),1) Nodes(EC(:,5),1) Nodes(EC(:,2),1) Nodes(EC(:,8),1) Nodes(EC(:,3),1) Nodes(EC(:,11),1) ]; % X-Coordinate MAtrix NEx3 Y=[Nodes(EC(:,1),2) Nodes(EC(:,5),2) Nodes(EC(:,2),2) Nodes(EC(:,8),2) Nodes(EC(:,3),2) Nodes(EC(:,11),2) ]; % Y-Coordinate MAtrix NEx3 Z=[Nodes(EC(:,1),3) Nodes(EC(:,5),3) Nodes(EC(:,2),3) Nodes(EC(:,8),3) Nodes(EC(:,3),3) Nodes(EC(:,11),3) ]; % Z-Coordinate MAtrix NEx3 %c=ones(NE,1); Xm=-X;Ym=Y;Zm=Z; % Mirrored Cooridinate Matrices to print the other half hold on; % to plot the following on the same graph fill3(X',Z',Y',CC1'); % Plot the first half fill3(Xm',Zm',Ym',CC1'); % Plot the second half