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