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Re: [Help-gsl] convergence check in odeiv_rk4imp ?


From: Forest Yang
Subject: Re: [Help-gsl] convergence check in odeiv_rk4imp ?
Date: Tue, 5 Jan 2010 18:34:18 -0500

Hi

  I was trying to evaluate the rk4imp solver at large step, but not
being able to do it on a fixed stepsize way.
Can I truely do rk4imp with a fixed time step ?

I used the following two lines, and also put a print line in f, the
time printed out have many steps between [t,t+h], Is it normal in the
internal stage when solving the fixed point or still an adaptive
stepsize control ?


 GSL_ODEIV_FN_EVAL(&sys, t, y, dydt_in);
 int status = odeiv2_step_apply (s, t, h, y, y_err, dydt_in, dydt_out, &sys);

Lingyun



On Thu, Dec 31, 2009 at 1:24 AM, Tuomo Keskitalo <address@hidden> wrote:
> Hello,
>
> take a look at my ode-initval2 extension to GSL, it's rk4imp iterates to
> convergence. Note: I'm currently working on finetuning the ode-initval2
> framework, it will soon change slightly from version 0.9.
>
> http://iki.fi/tuomo.keskitalo/gsl/ode-initval2/
>
> On 12/29/2009 08:35 PM, Forest Yang wrote:
>
>> Hi All,
>>
>>    Is there any plan for implementing convergence check in implicit
>> RK4 method ?
>> It seems the 2 stages Gauss points are only iterate 3 steps, without
>> checking whether it is converged or not.
>> Another possible way could be using the Jacobian to solve for "Y_i",
>> the fixed point.
>>
>>   The reason I care about this is, Implicit Gauss RK4 is symplectic,
>> which for Hamiltonian Dynamics simulation is a very important
>> property,
>> it has better conservation of the first integral.
>>
>>
>> Best regards,
>> Forest.
>>
>>
>> _______________________________________________
>> Help-gsl mailing list
>> address@hidden
>> http://lists.gnu.org/mailman/listinfo/help-gsl
>>
>
>
> --
> address@hidden
> http://iki.fi/tuomo.keskitalo
>




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