Roy Stogner wrote: > > > On Mon, 8 Dec 2008, jurak wrote: > >> I am using DifferentiableSystem class for some time now, together with >> EulerSolver class. Recently EulerSolver::element_residual() function >> was changed and now it calls _system.mass_residual() only once, instead >> of two >> times, as in 0.6.2 version. >> >> This has a side-effect that EulerSolver can now solve only equations >> linear in time >> derivative, that is, of the form >> dx/dt = F(x), >> while before one could also solve >> d/dt M(x) = F(x), >> with nonlinear M. The reason is that now the function forms residual >> R = dt F(x_theta) + M(x_old - x) >> while before it would form: >> R = dt F(x_theta) + M(x_old) - M(x). >> >> Is there any reason for this change except optimization? > > Yes; it was necessary to get correct results on moving-mesh problems > where the size of an element might change between x_old and x. > >> I would like to be able to treat nonlinearity in time derivative >> term. > > You might have to turn on and use the "elem_fixed_solution" which we > put in for use in stabilized formulations. That'll be equal to the > theta_solution in an EulerSolver run. > --- > Roy > I think that I understand.
By using "elem_fixed_solution" I get "x_theta = theta*x+(1-theta)*x_old", and from "elem_solution" I get " x_old - x". Then one can recover "x_old" and "x" and "mass_residual()" function calculates M(x_old) - M(x). Right? Mladen - <http://web.math.hr/%7Ejurak> ------------------------------------------------------------------------------ SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
