[X,Y]=meshgrid(0:0.01:pi,-1:0.01:1);
Z=Y.*sin(X);
Z(Y>cos(X))=NaN;
surf(X,Y,Z)
shading interp
hold on
C=-2/(3*pi);
contour3(X,Y,Z,[C C],'black')
xlabel('x','FontSize',12)
ylabel('y','FontSize',12)
zlabel('z','FontSize',12)
rotate3d on
colorbar
pause
surf(X,Y,C+0.*Z)
hold off