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Re: Help with ODE solver
From: |
Marco Antoniotti |
Subject: |
Re: Help with ODE solver |
Date: |
Thu, 12 Sep 2002 10:05:34 -0400 |
> From: Michael Hanke <address@hidden>
> Date: Thu, 12 Sep 2002 08:31:23 +0200
> Cc: address@hidden
>
> Hi:
>
> If I understand you correctly, the first property will defin itely not work.
> There are two reasons for that:
> 1. The identity t==t_i will almost never be fulfilled because the integration
> routine adapts the values where f is called according to your problem and
> accuracy requirements. Even if it would take t_i theoretically, equality is
> very unlikely to be fulfilled because of possible rounding errors. In short:
> Never check floating point numbers for equatlity!
Of course. I should have thought of that. Thanks for pointing it
out.
>From what you say I surmise that LSODE is an adaptive step integration
method, isn't it? If so then I will definitively not be able to do
the check even if I tested something like
if (abs(t - t_i) <= some_epsilon)
> 2. Changing state variables leads to a discontinuity in the right hand side
> of your problem. This will lead to a breakdown of the control structures.
> Most common, you will obtain stepsize underflow near t_i. You must give the
> code a chance to reinitialize. This is only possible with the second
> approach.
Ok. Thanks a lot this clears the mist. It is just more work to do
so.
regards
--
Marco Antoniotti ========================================================
NYU Courant Bioinformatics Group tel. +1 - 212 - 998 3488
715 Broadway 10th Floor fax +1 - 212 - 995 4122
New York, NY 10003, USA http://bioinformatics.cat.nyu.edu
"Hello New York! We'll do what we can!"
Bill Murray in `Ghostbusters'.
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-------------------------------------------------------------
- Help with ODE solver, Marco Antoniotti, 2002/09/11
- Re: Help with ODE solver, Michael Hanke, 2002/09/12
- Re: Help with ODE solver, Douglas Eck, 2002/09/12
- Re: Help with ODE solver, John W. Eaton, 2002/09/12
- Re: Help with ODE solver, Marco Antoniotti, 2002/09/12
- Message not available
- Re: Help with ODE solver, John W. Eaton, 2002/09/12
- Re: Help with ODE solver, Marco Antoniotti, 2002/09/12
- Re: Help with ODE solver, John W. Eaton, 2002/09/12
- Re: Help with ODE solver, Marco Antoniotti, 2002/09/12
- Re: Help with ODE solver, John W. Eaton, 2002/09/12
- Re: Help with ODE solver, Marco Antoniotti, 2002/09/13
- Re: Help with ODE solver, John W. Eaton, 2002/09/13