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MathGroup Archive 1999

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Re: PlotVectorField Package (easy question?)

  • To: mathgroup at smc.vnet.net
  • Subject: [mg15904] Re: [mg15838] PlotVectorField Package (easy question?)
  • From: BobHanlon at aol.com
  • Date: Wed, 17 Feb 1999 23:33:46 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

In a message dated 2/12/99 8:44:54 PM, ami at teleport.com writes:

>I am running Mathematica 3.0 on a G3, and having trouble using
><<Graphics`PlotVectorField`
>
>******************************
>In[55]:=
>
><<Graphics`PlotField`
>
>In[56]:=
>    (PlotGradientField[{2  x^2 + y, 3 x - y}, {x,-10,10 }, {y,-10,10}]
>
>Out[56]=
>
> "Graphics`PlotField`PlotVectorField[ 
>    	{{4 x, 3}, {1, -1} , {x, -10, 10}, {y, -10, 10},
>		{A long list of all the options}] 
>     
>
>******************    
>??PlotGradientField gives the help information from the package, but it
>still won't plot.  ??PlotVectorField returns: Global['PlotVectorField']
>
>I have tried clearing everything, running from inside PlotField.m, and
>even evaluating the example pages from the help manual. 
>PlotVectorField just won't run.  What am I doing wrong?
>

Adam,

Needs["Graphics`PlotField`"];

PlotGradientField[{2  x^2 + y, 3 x - y}, {x,-10,10 }, {y,-10,10}]

PlotVectorField[{{4*x, 3}, {1, -1}}, {x, -10, 10}, 
  {y, -10, 10}, {ScaleFactor -> Automatic, 
   ScaleFunction -> None, MaxArrowLength -> None, 
   ColorFunction -> None, AspectRatio -> Automatic, 
   HeadScaling -> Automatic, HeadLength -> 0.02, 
   HeadCenter -> 1, HeadWidth -> 0.5, 
   HeadShape -> Automatic, ZeroShape -> Automatic, 
   AspectRatio -> GoldenRatio^(-1), Axes -> False, 
   AxesLabel -> None, AxesOrigin -> Automatic, 
   AxesStyle -> Automatic, Background -> Automatic, 
   ColorOutput -> Automatic, DefaultColor -> Automatic, 
   Epilog -> {}, Frame -> False, FrameLabel -> None, 
   FrameStyle -> Automatic, FrameTicks -> Automatic, 
   GridLines -> None, ImageSize -> Automatic, 
   PlotLabel -> None, PlotRange -> All, 
   PlotRegion -> Automatic, Prolog -> {}, 
   RotateLabel -> True, Ticks -> Automatic, 
   DefaultFont :> $DefaultFont, 
   DisplayFunction :> $DisplayFunction, 
   FormatType :> $FormatType, TextStyle :> $TextStyle, 
   PlotPoints -> Automatic}]

The output from your call to PlotGradientField shows that Mathematica 
took the gradient of your input (i.e., a vector) and called PlotVectorField 
with the resulting matrix.  However, since PlotVectorField was expecting 
a vector function as input rather than a matrix it was unable to evaluate.

?PlotVectorField

PlotVectorField[f, {x, x0, x1, (xu)}, {y, y0, y1, (yu)},
   (options)] produces a vector field plot of the
   two-dimensional vector function f.

That is, PlotGradientField is expecting an input of a scalar function rather 
than the vector function which you provided.

?PlotGradientField

PlotGradientField[f, {x, x0, x1, (xu)}, {y, y0, y1, (yu)},
   (options)] produces a vector field plot of the gradient
   vector field of the scalar function f by calculating its
   derivatives analytically.

Perhaps you were intending to use PlotVectorField on your vector input

PlotVectorField[{2  x^2 + y, 3 x - y}, 
	{x,-10,10 }, {y,-10,10}];


Bob Hanlon


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