Re: Parametric Plot

• To: mathgroup at smc.vnet.net
• Subject: [mg27102] Re: Parametric Plot
• From: Brian Higgins <bghiggins at ucdavis.edu>
• Date: Sun, 4 Feb 2001 02:58:28 -0500 (EST)
• References: <95gma2\$8ir@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Winston, The problem is the extra braces that got carried along in the
calculation.
In[35]:={xd[t], xr[t]}

Out[35]={{InterpolatingFunction[{{0., 5000.}}, "<>"][
t]}, {InterpolatingFunction[{{0., 5000.}}, "<>"][t]}}

Plot does not worry about the extra braces but ParametricPlot cannot
interpret the expression for plotting with the extra braces. The
solution is to wrap the expresion with Flatten (and also with Evaluate
if you want to avoid uncompiled message)

ParametricPlot[Evaluate[Flatten[{xd[t], xr[t]}]], {t, 0, 100}]

Cheers

Brian

In article <95gma2\$8ir at smc.vnet.net>,
Winston Garira <uceswga at ucl.ac.uk> wrote:
> I am trying to solve a system of two coupled pendulums using the
NDSolve.
> command. If I replace the Plot[{xd[t],xr[t]},{t,0,100}] with
> ParametricPlot[{xd[t],xr[t]},{t,0,100}] it does not work. Can someone
tell
> me why the ParametricPlot command does not work in this case. I need
to
> make parametric plots for this system.
>
> Thanking you in annticipation
>
> Winston
>
>  Pends[init1_, init2_, time_, k_, {c_, w_, p_}]:=
>  Module[{},
> 	pend=NDSolve[{x1''[t]+ c x1'[t]+ p Sin[x1[t]]==k(x2[t]-x1[t]),
> 		      x2''[t]+ c x2'[t]+ p Sin[x2[t]]==k(x1[t]-x2[t]),
> 		x1[0]==init1[[1]], x1'[0]==init1[[2]],
> 		x2[0]==init2[[1]], x2'[0]==init2[[2]]},
> 		{x1, x2},
> 		{t,0,time}, MaxSteps->200000];
> 	xd[t_] := Evaluate[x1[t] /. pend];
> 	xdd[t_]:= Evaluate[x1'[t] /. pend];
> 	xr[t_] := Evaluate[x2[t] /. pend];
> 	xrd[t_]:= Evaluate[x2'[t] /. pend];
> 	];
>
> c=0.1; w=0.5; p=1.9;
>
> Pends[{1.57,0}, {-1.57,0}, 5000,0.6,  {c,w,p}];
> Plot[{xd[t],xr[t]},{t,0,100},
> PlotStyle\[Rule]{RGBColor[1,0,0.3],RGBColor[0,0.5,1]}];
>
> W.GARIRA
> E-mail: w.garira at ucl.ac.uk
> phone : +44-(0)20-7679-2521
> __________________________________________________

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```

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