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As is the case with Maple-detected errors, the computation is then interrupted and aborted.
11.7.2 lasterror and traperror
The variable lasterror records the most recent kind of ERROR. The function traperror evaluates an
expression sequence and returns the value if there were no errors, or lasterror if there was an error.
You can use these two features in combination to control error handling yourself instead of just having
Maple interrupt and abort processing.
11.8 Plotting Functions You Have Created
Now that you have learned how to write Maple functions you can effectively plot 3-dimensional graphs
(assuming you are in an X-session). The command is plot3d. You specify a set of functions to plot and
the ranges of the independent variables. The functions must satisfy the characteristics described in
?plot3d, but with some thought you can plot almost any kind of surface in 3-space. You can also give
plot options to configure various aspects of the final display. Here is a lengthy example of how to plot
parametric functions using plot3d. You can enter it interactively or place the commands in a file and
read it in.
> x1 := proc(tau, theta)
> (a + b*sin(tau))*cos(theta);
> end:
> y1 := proc(tau, theta)
> (a + b*sin(tau))*sin(theta);
> end:
> z1 := proc(tau, theta)
> b*cos(tau);
> end:
> torus1 := [x1,y1,z1]:
> x2 := proc(tau, theta)
> a + x1(tau, theta);
> end:
> y2 := proc(tau, theta)
> z1(tau, theta);
> end:
> z2 := proc(tau, theta)
> y1(tau, theta);
> end:
> torus2 := [x2, y2, z2]:
> plotranges := 0..2*Pi, 0..2*Pi:
> optionseq := scaling=CONSTRAINED, axes=NONE, numpoints=1600:
> plotboth := 'plot3d({torus1, torus2}, plotranges, optionseq)':
> a := 10: b := 3:
> # Now just use "plotboth" to plot the two surfaces
> plotsetup (window);
> plotboth;
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