[aspect-devel] Skip "cheap" solver phase for Stokes system

[Wolfgang Bangerth]

All,
Ian Rose asked yesterday whether there is a way to skip the 30 "cheap" 
Stokes solver iterations that are attempted at the beginning using a 
"cheaper" preconditioner (details in the Aspect paper, GJI 2012). Trying 
this cheaper preconditioner turns out to be a useful strategy for models 
with constant viscosity, but it's not so successful if you have a 
spatially variable viscosity for which these preconditioners don't work 
so well.

In any case, long story short, there is now a top-level parameter
   Number of cheap Stokes solver steps
that defaults to the traditional 30 but can be set to any other value as 
well, including zero -- in the latter case skipping the attempt of using 
the cheap preconditioner altogether.

Best
  Wolfgang
-- 
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Wolfgang Bangerth               email:            bangerth at math.tamu.edu
                                 www: http://www.math.tamu.edu/~bangerth/