Re: NDSolve and Parametric Plot

*To*: mathgroup at smc.vnet.net*Subject*: [mg85445] Re: [mg85430] NDSolve and Parametric Plot*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Mon, 11 Feb 2008 06:03:20 -0500 (EST)*Reply-to*: hanlonr at cox.net

Delete the outer braces solution = NDSolve[{x'[t] == 2 p[t], x[0] == 2, p'[t] == -2 x[t], p[0] == Sqrt[-3]}, {x, p}, {t, 0, Pi}][[1]]; repart[t_] := Re[x[t] /. solution] impart[t_] := Im[x[t] /. solution] ParametricPlot[{repart[t], impart[t]}, {t, 0, Pi}, PlotRange -> {{-2, 2}, {-2, 2}}] This can also be solved exactly solution = DSolve[{x'[t] == 2 p[t], x[0] == 2, p'[t] == -2 x[t], p[0] == = Sqrt[-3]}, {x, p}, t][[1]] {x -> Function[{t}, 2*Cos[2*t] + I*Sqrt[3]*Sin[2*t]], p -> Function[{t}, I*(Sqrt[3]*Cos[2*t] + 2*I*Sin[2*t])]} Bob Hanlon ---- Alex Cloninger <acloninger at wustl.edu> wrote: > So I'm trying to run a simple program that will solve this series of diff= erential equations and plot the the x[t] function in the complex plane. He= re's my code. > > solution = NDSolve[{x'[t] == 2p[t], x[0] == 2, p'[t] == -2x= [t], p[0] == Sqrt[-3]}, {x, p}, {t, 0, 2*=CF=80}] > > repart[t_] := Re[x[t] /. solution] > impart[t_] := Im[x[t] /. solution] > > ParametricPlot[{repart[t], impart[t]}, {t, 0, 2=CF=80}, PlotRange -> {{-2= , 2}, {-2,2}}] > > For some reason, when I go to plot the curve, I get an error saying > ParametricPlot::pptr: {repart[t], impart[t]} does not evaluate to a pair = of real numbers at t=2.617993877991494`*^-7 > > What's going on? Could someone please help me with this? >