Hi Ruben,
regarding your GSL question, take a look here: http://lists.gnu.org/archive/html/help-gsl/2012-06/msg00036.html <http://lists.gnu.org/archive/html/help-gsl/2012-06/msg00036.html> It shows how the jacobian is stored. I hope this helps. — Juan Pablo > On 23 Apr 2015, at 00:30, Ruben Farinelli <ruben.farine...@gmail.com> wrote: > > Hi, > I have been working for a long time on a complicate physical problem. > I have a set of ODEs, three of which are first-order, and the fourth > is of second order. > In the latter case unfortunately, I have conditons for its derivative > R'[0]=0, > while the second is actually an asymptotic boundary condition, namely > the function must tend to zero for large value of the variable. > Of course with a change of variable the system becomes N+1 > first order ODEs. > > Actually I have implemented some kind of shooting method, the main > issue is that the function has an exponential-decay behavior and > the result seems to be rather dependent on the adopted integrator. > > Finally I decided to compute the complicate Jacobian to test > the gsl_odeiv_bsimp which I read should be the most powerful. > > A-part from any welcome suggestion in approaching BVPs, I have > a doubt. Namely, the right-hand side of the system contains not only > the functions y_i but also their first derivatives, labeled F_i, or y'_i. > I mean something like > > F[0]=f_0{y[0]...y[n], F[1].....F[n]} > F[1]=f_1{y[0]...y[n], F[0].....F[n]} > etc etc > > The GSL jacobian function arguments are > (double t, const double y[], double *dfdy, double dtdy[], void *params) > > but I don't see where the functions derivative y'_i are stored. > They are still present when computing the Jacobian, but apparently > they are not read. > > Is there something wrong ? > > Thank you for your help ! > Ruben