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Re: [Bug-gsl] [bug #30540] please, add convergence checks in rk4imp/rk2i
Sergey B Kirpichev
Re: [Bug-gsl] [bug #30540] please, add convergence checks in rk4imp/rk2imp
Thu, 2 Sep 2010 15:26:01 +0400
On 8/27/10, Tuomo Keskitalo <address@hidden> wrote:
> A quick comment: You need to specify the function for calculating the
> Jacobian for sys-henon, the new implicit codes require it. Please look
> at documentation in doc/ode-initval.texi. Use of fixed step size is
> similar to old ode-initval.
Right. Fixed version (with jacobian, attached below) seems to be working.
Actually, it works only for eps_abs ~ round off error. Already for
eps_abs = 1e-10 it's easy to see small (linear?) drift in hamiltonian
from the constant.
Why mix step size control tolerances and root-finding tolerances?
Why not just use prefered fixed value of eps_abs for root-finding
(e.g.: GSL_DBL_EPSILON), as does attached patch for bug #30540 or
other implicit solvers (e.g.
http://www.unige.ch/~hairer/prog/stiff/radau5.f), but instead
complicate low level solver routines?
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- Re: [Bug-gsl] [bug #30540] please, add convergence checks in rk4imp/rk2imp,
Sergey B Kirpichev <=