Re: NDSolve - Nice function but stiffness-problem

• To: mathgroup at smc.vnet.net
• Subject: [mg96472] Re: NDSolve - Nice function but stiffness-problem
• From: "slawek" <human at site.pl>
• Date: Sat, 14 Feb 2009 03:10:10 -0500 (EST)
• References: <gh8hih\$qv5\$1@smc.vnet.net> <ghb04q\$ok5\$1@smc.vnet.net>

```U¿ytkownik "Alois Steindl" <Alois.Steindl at tuwien.ac.at> napisa³ w wiadomo¶ci
news:ghb04q\$ok5\$1 at smc.vnet.net...
> Hello,
> I would guess, that Mathematica uses some kind of shooting algorithm to
> solve
> the BVP. Since the solutions of your ODE can become infinite at finite
> time, because the right hand side increases rapidly with f(x), the
> shooting algorithm isn't adequate for these problems. Collocation
> methods (like bvp4c in another system) work fine with these examples.

This ODE has finite solutions for finite time. Never derivative D[f[x],x] is
inifite for finite f[x].

BTW,

Substitute f[x] -> Log[g[x]]/A

D[Log[g[x]]/A,x] == g[x]

D[g[x],x]/g[x]/A == g[x]

D[g[x],x] == A g[x]^2

slawek

```

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