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Re: ContourPlot doesn't work properly?


I get the message

ContourGraphics::ctpnt:
    The contour is attempting to traverse a cell in which some of the
    points have not evaluated to numbers, and it will be dropped.

and an empty frame for both of your examples.Which is understandable because
Log[y] is complex when x<0 and not defined when x=0.
However

ContourPlot[Log[y]-x,{x,-10,10},{y,0.001,10},
PlotPoints->30,Contours->{0},ContourShading->False]

works shows a curve.

Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

"Higinio Ramos Calle" <higra at gugu.usal.es> wrote in message
news:8hsucc$dhq at smc.vnet.net...
>
> Let's take a common function like y=Exp[x]
> If I try to make a picture of this function in an implicit way with
> ContourPlot in the form
> ContourPlot[Log[y]-x,{x,-10,10},{y,-10,10},
> PlotPoints->30,Contours->{0},ContourShading->False]
>
> with the option PlotPoints->30 in order to have a more precise picture I
> obtain an error message:
>
>     ContourGraphics::ctpnt:
>
>     The contour is attempting to traverse a cell in which some of the
>
>     points have not evaluated to numbers, and it will be dropped.
>
> and no picture.
>
> But if I let the option PlotPoints his default value the message is the
> same, but now the picture is drawn.
>
> Could anyone explain what happens?
>
> higra at gugu.usal.es
>




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