Re: NDSolve Singularity

• To: mathgroup at smc.vnet.net
• Subject: [mg85552] Re: NDSolve Singularity
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Wed, 13 Feb 2008 06:57:50 -0500 (EST)
• Organization: Uni Leipzig
• References: <foucd4\$l15\$1@smc.vnet.net>

```Hi,

if you look at your equations you see that the equation for
r[t] include a term

r'[t]== .. + 40.3234 * r[t] + ..

and this must explode because it gives
r[t] proportional to Exp[40.3234 *t]

So there is only one solution .. solve other equations
I would suggest {r'[t]==0,y'[t]==0}
or fix you equations / parameters.

Regards
Jens

Tara.Ann.Lorenz at gmail.com wrote:
> Hello,
>
> The following input for NDSolve is giving me a "singularity" error
> (see error message below).  As a result, my system of equations is
> being solved until the singularity at t=0.179 and not until t=30 as
> desired.  Any suggestions on how to avoid this issue?  Thank you!
>
> va = 4.71*y[t] - 246;
> q = 6;
> kl = 5;
> kt = 40;
> b = 760;
> mrco2 = 250;
> caco2 = 48 + 6*(paco2 - 40)/7;
> paco2 = (b - 47)*r[t];
> fico2 = 0.07;
> grodinstime0to30 =
>  NDSolve[{r'[
>      t] == (1/
>        kl)*((fico2*va + 8.63*q*(y[t] - caco2)/(b - 47) - r[t]*va)),
>    y'[t] == (mrco2 + 10*q*(caco2 - y[t]))/(10*kt), r[0] == 0.058,
>    y[0] == 0.533}, {r, y}, {t, 0, 30}]
>
>
> ERROR MESSAGE:
> NDSolve::ndsz: At t == 0.17926445744166167`, step size is effectively
> zero; singularity or stiff system suspected. >>
>
>
>
>
>
>

```

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