On Wed, Sep 12, 2018 at 5:16 PM Smith, Barry F. <[email protected]> wrote:
> > The function norm given by the -snes_monitor is the function norm for > the DVI problem (which depends on where the solution is constrained) while > FormFunction() norm you compute is for the original unconstrained problem. > > I am still not sure why you solve this as a DVI. If you solve it > without the constraints do you get the "wrong" answer? > If this is a variational crack problem, you can solve it unconstrained if you use a quadratic penalty term. However, that induces spurious long range communication between crack tips. If you bound the phase field between 0 and 1, you can use a linear penalty which has physical behavior. Matt > Barry > > > > On Sep 12, 2018, at 3:32 PM, Josh L <[email protected]> wrote: > > > > Hi, > > > > my solution is mostly very close to 1. only for a very small area where > solution goes from 0 to 1(a smeared crack). > > > > I set -snes_atol 1e-7 and it is converging. > > > > I've noticed the following: > > > > There is a difference between the function norm. > > > > I calculate the function norm in FormFunction, so every time it is > called it gives the function norm > > , and the result is different from the function norm given by > -snes_monitor if i set > > > > SNESSetType(snes,SNESVINEWTONRSLS,ierr) > > SNESVISetVariableBounds(snes,xl,xu,ierr) > > > > The function norm calculated in FromFunction is NOT reducing, however, > the function norm given by -snes_monitor is reducing > > They are the same if I just use regular SNES without setting variable > bounds. > > > > > > Thanks, > > Josh > > > > 2018-09-12 12:02 GMT-05:00 Smith, Barry F. <[email protected]>: > > > > You have too tight a convergence tolerance for your problem. You > can't expect to get more than 1.e-12 as the minimum residual norm or even > less. > > > > How close is your solution to 1 and -1? > > > > If you really need much higher convergence you can try ./configure > --with-precision=__float128 > > > > > > Barry > > > > > On Sep 11, 2018, at 11:53 PM, Josh L <[email protected]> wrote: > > > > > > Yes, I initialize all u_i to 1.0 > > > > > > > > > > > > 2018-09-11 23:37 GMT-05:00 Smith, Barry F. <[email protected]>: > > > > > > Do you start with initial conditions of 0 <= u_i <= 1 ? > > > > > > Run with -snes_monitor -snes_converged_reason > -ksp_monitor_true_residual -info -snes_linesearch_monitor and send all the > output > > > > > > Barry > > > > > > > > > > On Sep 11, 2018, at 11:33 PM, Josh L <[email protected]> wrote: > > > > > > > > Hi, > > > > > > > > I am using SNES to solve an nonlinear equation f(u), and I know all > the u_i should be 0 and 1. > > > > > > > > First, I use SNES without constraint, and it converges. > > > > > > > > But, If I set > > > > SNESSetType(snes,SNESVINEWTONRSLS,ierr) > > > > SNESVISetVariableBounds(snes,xl,xu,ierr) > > > > > > > > where xl and xu is vector, and xl_i=0 and xu_i=1 > > > > > > > > then SNES fails to converge, because linesearch fails(snes reason = > -6), and the norm of residual is not reducing(the norm of incremental > solution is reducing) > > > > > > > > The reason to add constraint is that I want to implement some > irreversibility. > > > > > > > > > > > > Thanks, > > > > Josh > > > > > > > > > > > > > > > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
