[Bug-gsl] Error in manual: forcing ode minimum step size

[Taneli Kalvas]

The manual has the following comment and suggestion for ODE evolve:

Evolving the system directly through a discontinuity with a strict 
tolerance may result in extremely small steps being taken at the edge of 
the discontinuity (e.g. down to the limit of machine precision). In this 
case it may be necessary to impose a minimum step size hmin suitable for 
the problem:

     while (t < t1)
     {
        gsl_odeiv_evolve_apply (e, c, s, &sys, &t, t1, &h, y);
        if (h < hmin) { h = hmin; } ;
     }

The value of h returned by gsl_odeiv_evolve_apply is always a suggested 
value and can be modified whenever needed.

--

I find that this is untrue as gsl_odeiv_evolve_apply will use the 
control function to modify the step size. The starting h is only a 
suggestion to the function. This example is wrong as it will not force a 
minimum.

Still... it would be nice to have a possibility for forcing a minimum 
step size.

Taneli

--
Taneli Kalvas
M.Sc., Researcher
Department of Physics, room FL114
P.O. Box 35 (YFL)
40014 University of Jyväskylä, Finland
Phone:  +358-14-260-2456
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