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MathGroup Archive 2007

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Re: weird behavior when plotting multiple functions in 6.0

  • To: mathgroup at smc.vnet.net
  • Subject: [mg76267] Re: weird behavior when plotting multiple functions in 6.0
  • From: Roman <rschmied at gmail.com>
  • Date: Fri, 18 May 2007 06:30:15 -0400 (EDT)
  • References: <f2btov$iga$1@smc.vnet.net>

Hello all,
Here's my attempt at a workaround, defining a plotting function which
will color things properly. I've tried to list all relevant elements
of Options[Plot] in the rules for the mock Plot[] call, and removed
those like Filling which give warnings, but have not tested this very
much yet.

MultiPlot[f_, R_, opts:OptionsPattern[]] :=
   Module[{x, X, Y, Z},
      (* extract the name of the abscissa variable *)
      x = {R}[[1, 1]];
      (* mock plotting, evaluating the function f[x] with adaptive
algorithm *)
      X = Reap[Plot[Sow[{x, f}][[2]], R, Evaluate[FilterRules[{opts},
                {Evaluated -> Automatic, EvaluationMonitor -> None,
                 Exclusions -> Automatic, MaxRecursion -> Automatic,
                 Method -> Automatic, PerformanceGoal :>
$PerformanceGoal,
                 RegionFunction -> (True &), WorkingPrecision ->
MachinePrecision}]]]][[2, 1]];
      (* drop the attempted analytical evaluations and sort *)
      Y = Sort[Cases[X, {_Real, _}]];
      (* extract abscissa values *)
      Z = Transpose[Y][[1]];
      (* replot with proper coloring *)
      ListLinePlot[Transpose[{Z, #}]&/@Transpose[Transpose[Y][[2]]],
         Evaluate[FilterRules[{opts}, Options[ListLinePlot]]]]]
SetAttributes[MultiPlot, HoldAll]

You can see the difference here:
f[x_?NumericQ] := {Sin[x], Cos[x], Tan[x]}
Plot[f[y], {y, 0, 2*Pi}, PlotRange -> {-2, 2}, Filling -> {1 -> 0, 2 -
> -2, 3 -> 1}]
MultiPlot[f[y], {y, 0, 2*Pi}, PlotRange -> {-2, 2}, Filling -> {1 ->
0, 2 -> -2, 3 -> 1}]

Any opinions on the above code?

Cheers!
Roman.

On May 15, 11:16 am, Roman <rschm... at gmail.com> wrote:
> Hello all:
>
> When I plot
>     Plot[{Sin[x], Cos[x]}, {x, 0, 4*Pi}]
> I get two curves: one blue, one red.
>
> But when I do
>     f[x_] = {Sin[x], Cos[x]};
>     Plot[f[x], {x, 0, 4*Pi}]
> both curves are blue. It is as if at some level Mathematica does not
> understand that I'm actually plotting two curves at a time, and uses
> the first color specification (blue) for both curves.
>
> This is particularly annoying when you want to play with plot styles,
> for example filling instructions, like
>     Filling -> {1 -> -1, 2 -> 1}
> which works in the first example but not in the second one.
>
> Has anyone figured out a workaround for this one?
>
> Thanks!
> Roman.




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