Plot not working correctly
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From: Magbenji on 13 Mar 2010 07:56 Hello, I'm having a problem with plotting and I'm not sure what the cause of it is. What is going on??? Here is what I'm doing: (*A simple system of ODEs*) dS[t_]:= -b/P*S[t]*Inf[t] dInf[t_]:=b/P*S[t]*Inf[t]-g*Inf[t] dR[t_]:=g*Inf[t] (*A function to solve the system and return the value of R[100000]*) ar[r_,s_,pop_]:=Module[{parms,solution}, parms={P->pop,b->r,g->s}; solution= NDSolve[{S'[t]==dS[t],Inf'[t]==dInf[t],R'[t]==dR[t],S[0]==P-1,Inf[0]==1,R[0]==0}/.parms, {S,Inf,R},{t,0,100000}]; (R[x]/pop /.solution /. x->100000)[[1]] ] (*Use ListPlot to look at values; works correctly*) ListPlot[Table[{i,ar[0.1,i,10000]},{i,0,0.1,0.001}],PlotLabel- >"CORRECT"] (*Now try it using Plot; WRONG PLOT*) Plot[ar[0.1,x,10000],{x,0,0.1}, PlotLabel->"INCORRECT"]
From: Bob Hanlon on 14 Mar 2010 06:16 You used x inside the definition of ar[ ] without localizing it to the Module. This conflicts with the x used in the Plot. Bob Hanlon ---- Magbenji <ben.ridenhour(a)gmail.com> wrote: ============= Hello, I'm having a problem with plotting and I'm not sure what the cause of it is. What is going on??? Here is what I'm doing: (*A simple system of ODEs*) dS[t_]:= -b/P*S[t]*Inf[t] dInf[t_]:=b/P*S[t]*Inf[t]-g*Inf[t] dR[t_]:=g*Inf[t] (*A function to solve the system and return the value of R[100000]*) ar[r_,s_,pop_]:=Module[{parms,solution}, parms={P->pop,b->r,g->s}; solution= NDSolve[{S'[t]==dS[t],Inf'[t]==dInf[t],R'[t]==dR[t],S[0]==P-1,Inf[0]==1,R[0]==0}/.parms, {S,Inf,R},{t,0,100000}]; (R[x]/pop /.solution /. x->100000)[[1]] ] (*Use ListPlot to look at values; works correctly*) ListPlot[Table[{i,ar[0.1,i,10000]},{i,0,0.1,0.001}],PlotLabel- >"CORRECT"] (*Now try it using Plot; WRONG PLOT*) Plot[ar[0.1,x,10000],{x,0,0.1}, PlotLabel->"INCORRECT"] -- Bob Hanlon
From: dh on 15 Mar 2010 06:01
Hi, this has nothing to do with Plot. It is a matter of localization. In the ar modul you are using R[x] without localizing x. Therefore, the global x is used that already has a value different from what you want. Daniel On 13.03.2010 13:56, Magbenji wrote: > dS[t_]:= -b/P*S[t]*Inf[t] > dInf[t_]:=b/P*S[t]*Inf[t]-g*Inf[t] > dR[t_]:=g*Inf[t] > > (*A function to solve the system and return the value of R[100000]*) > > ar[r_,s_,pop_]:=Module[{parms,solution}, > parms={P->pop,b->r,g->s}; > solution= > NDSolve[{S'[t]==dS[t],Inf'[t]==dInf[t],R'[t]==dR[t],S[0]==P-1,Inf[0]==1,R[0]==0}/.parms, > {S,Inf,R},{t,0,100000}]; > (R[x]/pop /.solution /. x->100000)[[1]] > ] > > (*Use ListPlot to look at values; works correctly*) > > ListPlot[Table[{i,ar[0.1,i,10000]},{i,0,0.1,0.001}],PlotLabel- >> >"CORRECT"] > (*Now try it using Plot; WRONG PLOT*) > > Plot[ar[0.1,x,10000],{x,0,0.1}, PlotLabel->"INCORRECT"] > -- Daniel Huber Metrohm Ltd. Oberdorfstr. 68 CH-9100 Herisau Tel. +41 71 353 8585, Fax +41 71 353 8907 E-Mail:<mailto:dh(a)metrohm.com> Internet:<http://www.metrohm.com> |