Hi!
Presently Maxima wraps all plotted expression using
"coerce-float-fun' (plot.lisp). The wrapper catches lisp
errors and returns either floating point value or T
if expression is singular or not well defined.
This is more or less OK with 2D plotting. It seems that
plot2d is smart enough to ignore this non numerical values.
The only not quite well handled situation is the case
when plotted expression cannot be evaluated numerically,
e.g. contains unknown function or variable. In this
situation plot2d tries hard for quite long time
to build the plot and finally produces gnuplot error.
Situation with 3D plots isn't so good.
First, plot3d stores function values into array
with :element-type = double-float. At least
on CMUCL and GCL such array refuses to store
non numerical values such as T and signals lisp error.
Clisp accepts T into double-float array (I was not
able to find in CLHS what is the right behavior
according to ANSI standard). So it is enough to have
just one singular point to prevent plotting entirely.
Even with clisp we can't plot - plot3d produces wrong
maxima.gnuplot file and gnuplot refuses to draw it.
Ideally, some more sophisticated 3D plotting algorithm
is required which either skips singular point or
approximate value in it using nearby values.
Other quick and dirty solution is to make "coerce-float-fun"
return 0.0 instead of T for singular points.
Any ideas?
--
Vadim V. Zhytnikov
<vvzhy@mail.ru>
<vvzhy@netorn.ru>