object explicit

Once you have opened a Maxima session, load package **draw** and then set global variable **draw_renderer** to **vtk**:

load("draw") $ draw_renderer: 'vtk $

To read the documentation on object **explicit**, write the following sentence:

describe(explicit) $

A simple plot in 2D:

draw2d(explicit(u^2,u,-3,3)) $

Piece-wise function exported to png:

draw2d( terminal = png, color = green, dimensions = [400,300], xlabel = "X Axis", ylabel = "Y Axis", explicit(u^2,u,-2,2), explicit(sin(z),z,2,6)) $

Two curves with background color and legend:

draw2d( background_color = light_green, key = "Exponential func", color = blue, line_width = 2, explicit(exp(x),x,-1,3), line_width = 5, line_type = dashes, color = "#4567a5", key = "Cubic poly", explicit(%pi*x^3+sqrt(2)*x^2+10,x,0,3)) $

Logarithmic scale. There is a known bug here: if you don't see the curve in logarithmic scales, clic on the image to refresh it:

draw2d( dimensions = [300,500], logy = true, line_width = 3, color = yellow, explicit(exp(x),x,0.1,20), background_color = brown, grid = true) $

Filled function exported to PNG format:

load(distrib)$ draw2d( terminal = jpg, dimensions = [400,350], grid = true, key_pos = top_left, background_color = dark_grey, xlabel = "X Axis", ylabel = "Y Axis", filled_func = true, fill_color = light_blue, key = "Pr(-1 < X < 0)", explicit(pdf_normal(x,0,1),x,-1,0), key = "Pr(1 < X <2)", fill_color = "dark-blue", explicit(pdf_normal(x,0,1),x,1,2), filled_func = false, color = red, key = "Normal density N(0,1)", explicit(pdf_normal(x,0,1),x,-3,3) ) $

Geometric transformation of a 2d explicit curve:

th : %pi/6$ draw2d( xrange = [-2,5], yrange = [-1,6], explicit(x^2,x,-1,1), transform = [cos(th)*x - sin(th)*y + 3, sin(th)*x + cos(th)*y + 3, x, y], color = red, explicit(x^2,x,-1,1) )$

A simple red colored surface:

draw3d( color = red, explicit(exp(-x^2-y^2),x,-2,2,y,-2,0)) $

If you now press key **w**, you can see the wired structure of the surface:

To see the colored surface again, press now key **s**.

When option **enhanced3d** is not false, the surface is colored according to the actual **palette**. The behavior here is the same as in the Gnuplot case:

draw3d( background_color = green, enhanced3d = [sin(3*(x+y)),x,y], explicit(exp(-x^2-y^2),x,-2,2,y,-2,0) )$

Rendering three explicit colored surfaces, each with its own **palette**; with VTK, option palette is a local option, which is not the case with Gnuplot, where multiple palettes are not allowed within the same scene. Also, the third surface is assigned an **opacity** level of 0.6; **opacity** is an option not available for the Gnuplot renderer:

draw3d( enhanced3d = [sin(3*(x+y)),x,y], explicit(exp(-x^2-y^2),x,-2,2,y,-2,0), palette = [-23, 6, -3], explicit(exp(-x^2-y^2)+2,x,-2,2,y,0,2), palette = gray, opacity = 0.6, explicit(exp(-x^2-y^2)+4,x,-2,2,y,-2,2) )$

User defined palettes are also possible; in such cases, assign option **palette** a list of colors. The first color will be assigned to the points in the surface with the lowest level, according to **enhanced3d**, while the last color is assigned to the highest value, and the rest are conveniently interpolated. User defined palettes have been also incorporated for the Gnuplot renderer:

draw3d( background_color = light_green, palette = ["#ff0000", green, light_blue], enhanced3d = [sin(3*(x+y)),x,y], explicit(exp(-x^2-y^2),x,-2,2,y,-2,0) )$

Going one step further, we can vary the opacity from one point to another if instead of a list of colors we assign option palette a list of pairs formed by the color and the opacity level. In this example, red is 50% transparent and light blue 100% opaque:

draw3d( palette = [["#ff0000",0.5], [green,0.8], [light_blue,1]], enhanced3d = y, explicit(exp(-x^2-y^2),x,-2,2,y,-2,0), palette = color, enhanced3d = x, explicit(exp(-x^2-y^2)-1,x,-2,2,y,-2,2) )$

The number of points to be calculated before plotting an explicit surface can be controlled by options **xu_grid** and **yv_grid**. See also in this example that the default color is blue:

draw3d( xu_grid = 3, yv_grid = 3, explicit(x^2+y^2, x, -2, 2, y, -2, 0) )$

Draw's **transform** option is also available for explicit functions in VTK:

draw3d( explicit(x^2+y^2,x,-2,2,y,-2,2), color = yellow, opacity = 0.5, transform = [x, y, -z+5, x, y, z], explicit(x^2+y^2,x,-2,2,y,-2,2))$

Projecting an explicit surface onto a plane:

draw3d( color = cyan, explicit(exp(-x^2-y^2),x,-2,2,y,-2,0), color = yellow, transform = [x,z,z, x,y,z], explicit(exp(-x^2-y^2),x,-2,2,y,-2,0) )$

Two explicit surfaces with the same palette. In one of them, option **wired_surface** is set to **true**. In the VTK interface, option **wired_surface** is local, but global in the Gnuplot interface:

draw3d( enhanced3d = true, explicit(x^2+y^2+2,x,-1,1,y,-1,1), wired_surface = true, explicit(x^2+y^2,x,-1,1,y,-1,1) ) $

Isolines of z values (default scalars) on an **explicit** surface:

draw3d( isolines = true, line_width = 4, explicit(exp(-x^2-y^2),x,-2,2,y,-2,2))$

Isolines of user defined scalars. The syntax for **isolines** values is the same used by **enhanced3d**. When using the formula syntax, the names of the variables must be the same used in **explicit**:

draw3d( isolines = sin(x*y), line_width = 2, explicit(exp(-x^2-y^2),x,-2,2,y,-2,2)) $

We can visualize two scalar fields playing together with **isolines** and **enhanced3d**:

draw3d( enhanced3d = x+y, isolines = sin(x*y), line_width = 4, explicit(exp(-x^2-y^2),x,-2,2,y,-2,2)) $

Multiple slices of a scalar field. Remember: using the list syntax, the first element is the expression of the scalar field and the rest are the names of the three coordinates, which can be arbitrary named:

draw3d( isolines = [2/3*x^3-y^2*z-3*z, x, y, z], makelist(explicit(k,x,-2,2,y,-2,2), k, -2, 2))$

Orthogonal slices. The surfaces are colored according to scalar field **F(x,y,z)=2/3*x^3-y^2*z-3*z**, but isolines are plotted according to a translation of **F(x,y,z)**:

draw3d( enhanced3d=[2/3*x^3-y^2*z-3*z, x, y, z], isolines = [2/3*(x-2)^3-(y+3)^2*(z+1)-3*(z+1), x, y, z], line_width=4, /* XY-plane */ explicit(0,x,-2,2,y,-2,2), /* YZ-plane */ transform = [z,x,y+z,x,y,z], explicit(0,x,-2,2,y,-2,2), /* XZ-plane */ transform = [x,-z,y,x,y,z], explicit(0,x,-2,2,y,-2,2) )$

Isolines of an explicit surface are projected onto a plane:

draw3d( line_width = 2, enhanced3d = [x*y,x,y], palette = gray, isolines = true, explicit(sin(x)*cos(y),x,1,10,y,1,10), /* isolines projected on the plane */ enhanced3d = false, isolines = [sin(x)*cos(y),x,y], explicit(-5,x,1,10,y,1,10) ) $

Setting **terminal=stl**, Maxima creates a 3D scene in **stl** format. In this example, file maxima_out.stl is generated, which is later explored with
Paraview. Note that colors are lost in format **stl**:

draw3d( terminal = stl, cylinder([0,0,0],5,5,[0,1,0]), color = orange, cube(1/2, 5, 3, [7, 0, 0]), color = white, explicit(sin(x)+cos(y), x,-5,5,y,-5,5)) $

Also, we can explore the **stl** scene with the javascript magic of Three (rotate with left button, zoom in and out with right button, change position with wheel button):

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