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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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