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This section shows how to draw contours in 3d.

In this case, contour lines are added in the xy-plane. Two screen captures follow.

draw3d(color = green, explicit(20*exp(-x^2-y^2)-10,x,0,2,y,-3,3), yv_grid = 10, color = red, explicit(x+y,x,0,2,y,-5,5), contour_levels = 15, contour = base, surface_hide = true) ;

More contours.

draw3d(color = green, explicit(20*exp(-x^2-y^2)-10,x,0,2,y,-3,3), contour_levels = 15, contour = both, surface_hide = true) ;

Even more contours.

draw3d(terminal = eps_color, title = "This is the last contours example", explicit(20*exp(-x^2-y^2)-10,x,0,2,y,-3,3), contour_levels = 15, contour = map, surface_hide = true) ;

Absolute value of the gamma function.

gamma2(x,y):= block([re,im,g:gamma(x+%i*y)], re:realpart(g), im:imagpart(g), sqrt(re^2+im^2))$ draw3d(zrange=[0,6], xu_grid = 50, yv_grid = 50, surface_hide = true, contour = surface, contour_levels = [0,0.5,6], /* from 0 to 6 in steps of 0.5 */ color = cyan, /* uncomment next line if you want an eps file */ /*terminal = eps_color,*/ explicit(gamma2(x,y),x,-4,4,y,-2,2));

Absolute value of the polynomic function **z ^{3}+1** with enhanced color and contours.

z3(x,y):= abs((x+y*%i)^3+1)$ draw3d(surface_hide =true, color = green, contour = both, enhanced3d=true, explicit(z3(x,y),x,-10,10,y,-10,10) );

It is possible to fix the number of isolines setting option **contour_levels** to a positive integer number. The actual number of
levels can be adjusted to give simple labels, as in this example.

draw3d( surface_hide = true, color = green, explicit(exp(-x^2-y^2),x,-2,2,y,-2,2), contour = surface, contour_levels = 3);

Declare increments to isolines setting **contour_levels** to a list of the form **[init, incr, end]**.

draw3d( surface_hide = true, color = green, explicit(exp(-x^2-y^2),x,-2,2,y,-2,2), contour = surface, contour_levels = [0.1,0.1,1]);

It is also possible to select a certain number of fixed levels setting **contour_levels** to a set of numbers.

draw3d( surface_hide = true, color = green, explicit(exp(-x^2-y^2),x,-2,2,y,-2,2), contour = surface, contour_levels = {0.1,0.7,0.8});

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by Mario Rodríguez Riotorto