eknecronzontas writes: > The stepsize for finite-differencing in > gsl-1.8/multiroots/fdjacobian.c is specified by the > lines > > > double xj = gsl_vector_get (x, j); > > double dx = epsrel * fabs (xj); > > This is, of course mathematically correct. > Nevertheless, the behavior is less than ideal if one > of the elements of the vector 'x' is sufficiently > small. This occurs often if one component of the root > happens to be zero. If this occurs, then 'dx' can be > so small that one of the columns of the Jacobian is > identically zero. This immediately leads to NAN's > which are not easy to trace.
Hello, Thanks for your email. I agree the behavior is not good for small/zero x. Probably the best thing would be to signal an error if the step size goes to zero or the derivative overflows. I'll add a note to the documentation to make it clearer anyway. You can change the behavior with a new drop-in routine copying from multiroots/hybrid.c into your own application, no need to modify the source. -- Brian Gough Network Theory Ltd, Publishing the GSL Manual - http://www.network-theory.co.uk/gsl/manual/ _______________________________________________ Help-gsl mailing list Help-gsl@gnu.org http://lists.gnu.org/mailman/listinfo/help-gsl
