On Thursday April 29 2010 08:57:52 cutejeff wrote: > Question #107819 on DOLFIN changed: > https://answers.launchpad.net/dolfin/+question/107819 > > Status: Answered => Open > > cutejeff is still having a problem: > Thank you for your help. > > The PDE was derived using conservation of mass, but the results from > Fenics showed the mass actually kept growing with time. Because my > finite difference code doesn't grow, I consider my finite element code > got some problems somewhere. > > Interestingly, if I get rid of the (du/dx)^2 term in both Fenics and my > finite difference code, the results match each other. Because I haven't > seen any examples on manipulating the power of derivatives, I think it > might be the cause. I don't think I can take integration by parts for > v*(du/dx)^2*dx, I don't know what to do with it, except keep it in this > way.
Are you having (du/dx)^2 or d2u/dx2 as you state in your original question? If it is the latter we do integrate that by part in several demos, Poisson for example. But you have u^3*d2u/dx2 which makes the integration by parts non trivial. You need to get that correct in addition to Garth's suggestions, I think. Johan _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : [email protected] Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
