Re: i dont understand module.

• To: mathgroup at smc.vnet.net
• Subject: [mg46563] Re: i dont understand module.
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Mon, 23 Feb 2004 22:33:45 -0500 (EST)
• Organization: Universitaet Leipzig
• References: <c1ampd\$460\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Hi,

you multiply a NDSolve[] call with a Plot[] function call
and wonder that you get out nonsense ??

Insert a ";"

Module[{},
sol = NDSolve[{a'[t] == -0.1` a[t] x[t], b'[t] == -0.05` b[t] y[t],
x'[t] == -0.1` a[t] x[t] + 0.05` b[t] y[t],
y'[t] == 0.1` a[t] x[t] - 0.05` b[t] y[t], a[0] == 1, b[0] ==
1,
x[0] == 1, y[0] == 0}, {a, b, x, y}, {t, 0, 250}][[1]] ;
Plot[Evaluate[#[[2]][t] & /@ sol], {t, 0, 250},
PlotStyle -> Table[Hue[(k + 1)/6], {k, 4}], Frame -> True, Axes ->
False,
PlotLegend -> (#[[1]] & /@ sol), LegendPosition -> {1, -.35},
LegendShadow -> {0, 0}, ImageSize -> 400];]

and all works fine.

Regards
Jens

sean kim wrote:
>
> hello goup.
>
> I just don't get this. this code was posted while back by Bob Hanlon.
>
> All i did was to flank the routine by a module. i did so to minimize
> memory used. I was hoping that by keepign things local, i can minimize
> the resources used in the routine.
>
> In[1]:=
> Needs["Graphics`"];
>
> Module[{},
>   sol=NDSolve[{a'[t]==-0.1` a[t] x[t], b'[t]==-0.05` b[t] y[t],
>               x'[t]==-0.1` a[t] x[t]+0.05` b[t] y[t],
>               y'[t]==0.1` a[t] x[t]-0.05` b[t] y[t],
> a[0]==1,b[0]==1,x[0]==1,
>               y[0]==0}, {a,b,x,y},{t,0,250}][[1]]
>
>         Plot[Evaluate[#[[2]][t]& /@ sol],{t,0,250},
>           PlotStyle->Table[Hue[(k+1)/6],{k,4}], Frame->True,
> Axes->False,
>           PlotLegend->(#[[1]]& /@ sol), LegendPosition->{1,-.35},
>   ]
> above fails with the following error.
>
> Plot::plnr: sol is not a machine-size real number at t = \
> 0.000010416666666666666`.
>
> if i flank the module with Do loop, then I get recursion errors
>
> In[5]:=
> Needs["Graphics`"];
>
> Do[
>   Module[{},
>     sol=NDSolve[{a'[t]==-0.1` a[t] x[t], b'[t]==-0.05` b[t] y[t],
>                 x'[t]==-0.1` a[t] x[t]+0.05` b[t] y[t],
>                 y'[t]==0.1` a[t] x[t]-0.05` b[t] y[t],
> a[0]==1,b[0]==1,
>                 x[0]==1,y[0]==0}, {a,b,x,y},{t,0,250}][[1]]
>
>
>           Plot[Evaluate[#[[2]][t]& /@ sol],{t,0,250},
>             PlotStyle->Table[Hue[(k+1)/6],{k,4}], Frame->True,
> Axes->False,
>             PlotLegend->(#[[1]]& /@ sol), LegendPosition->{1,-.35},
>     ],
>   {iteration, 10}]
>
> \$RecursionLimit::reclim: Recursion depth of 256 exceeded.
>
> what's going on here?  and how do i fix it so that i can run it
> automatically?
>