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MathGroup Archive 2001

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Re: Parametric Plot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg27130] Re: [mg27077] Parametric Plot
  • From: Reza Malek-Madani <research at usna.edu>
  • Date: Sun, 4 Feb 2001 21:27:12 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Let First act on your definitions of xd, xdd, xr, xrd inside the Module:

xd[t_] := First[Evaluate[x1[t] /. pend]];
xdd[t_] := First[Evaluate[x1'[t] /. pend]];
xr[t_] := First[Evaluate[x2[t] /. pend]];
xrd[t_] := First[Evaluate[x2'[t] /. pend]];

The rest of your program works.

Reza.


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On Sat, 3 Feb 2001, Winston Garira 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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