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MathGroup Archive 2001

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RE: Parametric Plot

  • To: mathgroup at
  • Subject: [mg27121] RE: [mg27077] Parametric Plot
  • From: "Wolf, Hartmut" <Hartmut.Wolf at>
  • Date: Sun, 4 Feb 2001 02:58:56 -0500 (EST)
  • Sender: owner-wri-mathgroup at

-----Original Message-----
From: Winston Garira [mailto:uceswga at]
To: mathgroup at
Subject: [mg27121] [mg27077] Parametric Plot

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


 Pends[init1_, init2_, time_, k_, {c_, w_, p_}]:=
	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}];

E-mail: w.garira at
phone : +44-(0)20-7679-2521

Dear Winston,

the problem is that your interpolating functions don't return a real, but a
list containing a real. So

ParametricPlot[Join[xd[t], xr[t + Pi/2]], {t, 0, 100}, Compiled -> False];

might be something more to your like.

-- Hartmut Wolf

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