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MathGroup Archive 2000

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Re: ParametricPlot3D is buggy

  • To: mathgroup at smc.vnet.net
  • Subject: [mg25242] Re: ParametricPlot3D is buggy
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Sun, 17 Sep 2000 04:47:20 -0400 (EDT)
  • References: <8psgl7$a5r@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Will,
You have found a nice bug here - seems to be a fault in calculating the plot
range:

gr1 = ParametricPlot3D[{Cos[t]Cos[u], Sin[t]Cos[u], Sin[u]},
{t, 0, 2Pi}, {u, -Pi/2, Pi/2}, PlotPoints -> {7, 3}];

PlotRange[gr1] // Chop

{{-1.05, 1.05}, {0, 0}, {-1.05, 1.05}}

gr2 = ParametricPlot3D[{Cos[t]Cos[u], Sin[t]Cos[u], Sin[u]}, {t, 0,
        2Pi}, {u, -Pi/2, Pi/2}, PlotPoints -> {5, 3}];

PlotRange[gr2] // Chop

{{0, 0}, {0, 0}, {-1.05, 1.05}}

The following work all right.

Show[gr1, PlotRange -> All];

Show[gr2, PlotRange -> All];

--
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

"Will Self" <wself at msubillings.edu> wrote in message
news:8psgl7$a5r at smc.vnet.net...
> Can anyone explain this bug that appears in ParametricPlot3D
> in my version of Mathematica 4.0.2 on Windows 2000?
>
> -----------------------------------------------------------
>
> This works fine:
>
> ParametricPlot3D[{Cos[t]Cos[u], Sin[t]Cos[u], Sin[u]},
> {t, 0, 2Pi}, {u, -Pi/2, Pi/2}, PlotPoints -> {8, 3}]
>
> But this doesn't give a picture:
>
> ParametricPlot3D[{Cos[t]Cos[u], Sin[t]Cos[u], Sin[u]},
> {t, 0, 2Pi}, {u, -Pi/2, Pi/2}, PlotPoints -> {7, 3}]
>
> This works fine:
>
> ParametricPlot3D[{Cos[t]Cos[u], Sin[t]Cos[u], Sin[u]},
> {t, 0, 2Pi}, {u, -Pi/2, Pi/2}, PlotPoints -> {6, 3}]
>
> But this doesn't give a picture:
>
> ParametricPlot3D[{Cos[t]Cos[u], Sin[t]Cos[u], Sin[u]},
> {t, 0, 2Pi}, {u, -Pi/2, Pi/2}, PlotPoints -> {5, 3}]
>
> In this last case, not only do I not get a picture, if I go
> back and change the PlotPoints option to anything at all,
> in the same cell, I still get no picture.
>
> With PlotPoints set to {4, 3} I again get no picture, but
> surprisingly, with PlotPoings set to {3,3} I get a picture.
> Of course in this case the "sphere" has gone flat.
>
> Do other people experience this same phenomenon? I find it
> amazing and frustrating that ordinary things that have been part
> of Mathematica for a long time do not work correctly.
>
> Will Self
>
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.
>




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