plot: bug or ?



On 07.2007, Stavros Macrakis wrote:
> On 5/6/07, Valery Pipin <pip at iszf.irk.ru> wrote:
> > ... F(th,ti):=realpart(expand(bx(.92,cos(th))*exp(%i*ti)));
> > ...
> > (%i214) contour_plot(F(x,y),[x,0,%pi],[y,0,3*%pi]);
> >                  2
> > Is  1.0 - 1.0 cos (x)  positive or negative?
>
> Try quoting F(x,y), e.g. contour_plot( '( F(x,y) ), ...).  It is probably
> trying to evaluate F at the symbolic value (x,y).
Thanks for reply!  I have :

(%i366) contour_plot('(F(x,y)),[x,0,%pi],[y,0,3*%pi]);

Maxima encountered a Lisp error:

 Error during processing of --eval option "(cl-user::run)":

  The value ((MLIST SIMP) 0.0) is not of type DOUBLE-FLOAT.

Automatically continuing.
To reenable the Lisp debugger set *debugger-hook* to nil.

(%i367) contour_plot(F,[x,0,%pi],[y,0,3*%pi]);

Maxima encountered a Lisp error:

 Error during processing of --eval option "(cl-user::run)":

  The value ((MLIST SIMP) 0.0) is not of type DOUBLE-FLOAT.

Automatically continuing.
To reenable the Lisp debugger set *debugger-hook* to nil.
(%i368) 
So  I need to unlist the output of bx(.92,cos(th)) ?
Note:
(%i378) F(%pi/4,%pi/4);
Evaluation took 0.01 seconds (0.01 elapsed) using 335.930 KB.
(%o378) 		     [- .1694397727137777]

>
> As for the syntax error, I suspect that is unrelated; there is an extra ";"
> or "$" somewhere.
I put it to escape  further questions ;-)

best
V