b*d_(ln_phi2)/dx = (b / phi2) (d phi2 / dx) but because (1/phi2) appears outside the gradient, you still won't be able to handle this implicitly.
I would just write an explicit source term: b*log(phi2).grad.mag > On Jul 6, 2016, at 3:13 PM, Gopalakrishnan, Krishnakumar > <k.gopalakrishna...@imperial.ac.uk> wrote: > > Hello, > > One of the PDEs in my (1D) system has the following form, > > a*d_phi1/dx + b*d_(ln_phi2)/dx + c*d_(phi3)/dt == d > > i.e. the PDE is defined such that one of the spatial derivatives is with > respect to the natural logarithm of the field variable to be solved for. > > I don’t think a simple change of variables shall work here, since the field > variable phi2, appears in its ‘correct’ form where it couples with other > PDEs in the system, i.e. in another PDE of this system, we have the term > d_phi2/dx directly, i.e. without the logarithmic derivative. > > > Looking at FiPy’s general conservation formula that it handles, it seems that > this setup is not amenable to be ‘digested’ in the way the PDE is currently > written. > > Is there any other technique/trick that is possible, so as to massage this > non-conforming structure so as to re-cast it in FiPy compatible form ? > (ie. perhaps some other transformation, mapping or some other trick, maybe > ?). > > > Thanks and Regards > > Krishna > _______________________________________________ > fipy mailing list > fipy@nist.gov > http://www.ctcms.nist.gov/fipy > [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ] _______________________________________________ fipy mailing list fipy@nist.gov http://www.ctcms.nist.gov/fipy [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ]
