[Bug-gsl] [bug #30947] Please, include fixed step size control object for ode suite

[Sergey B Kirpichev]

Follow-up Comment #2, bug #30947 (project gsl):

> one important reason for the evolve level functions is to allow
> for variable step size.

No.  Just to allow adaptive step size control.  Why don't
consider the *evolve_apply with fixed step as just a special case?

> If you really require a fixed step size for the stepper level, then
> you can use the for loop around step_apply function shown in the manual.

Of cource, I can (it WAS noted in bugreport).  Sometimes it's just not
convinient, e.g. to use _different loops_ for fixed and variable step sizes.

> Also, I'm afraid that using your cfxd may not guarantee the use of a
> fixed step size; also evolve_apply can change the step length,
> so you might have to have a function something like
> "evolve_apply_fixed_step_size" to do the job.

Why?  fc_control_hadjust() always returns GSL_ODEIV_HADJ_NIL - there
is no reason to change step size.

See also thread in bug-gsl:
http://lists.gnu.org/archive/html/bug-gsl/2010-09/msg00001.html


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