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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: [mg76089] Re: [mg76050] weird behavior when plotting multiple functions in 6.0
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Wed, 16 May 2007 05:25:49 -0400 (EDT)
  • References: <200705150859.EAA17134@smc.vnet.net>

On 15 May 2007, at 17:59, Roman 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.
>
>

This is completely reasonable. Unless Mathemaitca sees and explicit  
List as the Head of the argument to be plotted it will use the  
algorithm for plotting  a single function. Actually, this shows an  
interesting change compared with Mathematica 5.2. In Mathematica 5.2  
your code will produce no plot at all: but only error messages. In  
Mathematica 6 you actually get a plot of two fucntions but colored  
inthe same way. In both versions the correct thing to do is:

f[x_] = {Sin[x], Cos[x]};
Plot[Evaluate[f[x]], {x, 0, 4*Pi}]

Andrzej Kozlowski




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