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MathGroup Archive 2007

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Re: NDSolve, Do loop, and Plot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg77296] Re: NDSolve, Do loop, and Plot
  • From: dh <dh at metrohm.ch>
  • Date: Wed, 6 Jun 2007 07:20:08 -0400 (EDT)
  • References: <f43ese$151$1@smc.vnet.net>


Hi,

here is your clean up code, assuming you have not version 6:

mysol[w_?NumericQ]:=

   NDSolve[{x'[t]\[Equal]-y[t]-x[t]^2,y'[t]\[Equal]w x[t]-y[t]^3,

         x[0]\[Equal]y[0]\[Equal]1},{x,y},{t,20}][[1]]

Do[Plot[Evaluate[{x[t],y[t]}/.mysol[w]],{t,0,20}],{w,2,4}]

hope this helps, Daniel



DBK wrote:

> This seems like it should be easy, but it is giving me problems. I am

> running some simulations and would like to simply substitute in a

> different parameter value (w below)  for each run of the simulation. I

> would then like to separately plot each variable (x and y below) for

> each simulation run with a different value for w. My code is below.

> When run, I get no error messages but no plot as well. I've tried

> pulling the Plot function out of the Do Loop but had no luck.

> 

> Also, related to this, is it possible to provide mathematica with

> specific values of w instead of a range of values? For example, say I

> want to evaluate the simulation at w=2,5, and 14 instead of 2,3,4 as

> below.

> 

> ClearAll["Global`*"];

> $TextStyle = {FontFamily -> "Arial", FontSize -> 12,

>    FontSlant -> "Italic"};

> Do[mysol[w] =

>   NDSolve[{x'[t] == -y[t] - x[t]^2, y'[t] == w x[t] - y[t]^3,

>     x[0] == y[0] == 1}, {x, y}, {t, 20}];

>  Plot[{Evaluate[x[t] /. mysol[w]], Evaluate[y[t] /. mysol[w]]}, {t, 0,

>     20}], {w, 2, 4}]

> 

> 




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