RE: Parametric Plot

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

```
-----Original Message-----
From: Winston Garira [mailto:uceswga at ucl.ac.uk]
To: mathgroup at smc.vnet.net
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

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
___________________________________________________

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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