transform_xy error: value NIL is not of type DOUBLE-FLOAT

>>>>> "Adrian" == Adrian Brown <abrown at seti.org> writes:

    Adrian> Hi all,
    Adrian> I was wondering if anyone can help me make this work?

    Adrian> wxplot3d([r,theta,sqrt(sin(theta))],[r,0,1],[theta,0,2*%pi],
    Adrian> [gnuplot_pm3d,true],
    Adrian> [gnuplot_preamble, "set pm3d
    Adrian> map"],[grid,1,1],[transform_xy,make_transform([r,theta,z],r*cos(theta),r*sin(theta),z)])$

    Adrian> The error I get is:

    Adrian> Maxima encountered a Lisp error:
    Adrian> The value NIL is not of type DOUBLE-FLOAT.

Maxima should definitely do a better job here than signal a lisp
error.  Could you file a bug about that with this example?

However, what is it are you trying to plot with sqrt(sin(theta))?
Since sin(theta) <= 0 for %pi <= theta <= 2*%pi, plot3d probably gets
an error from taking the sqrt of a negative number and not knowing how
to deal with that.

Ray