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



Hi all,

I was wondering if anyone can help me make this work?

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

The error I get is:

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

This is an error within transform_xy because when I remove the 
transform_xy is works fine.

Thanks for any help with this!

Adrian

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