[petsc-users] dof>1 vector tools

Edward Bueler elbueler at alaska.edu
Mon Nov 15 17:38:37 CST 2010


> ...
> > I guess I would want the loop to be replaced by
> > "DAVecScaleDOF(da,v,k,alpha)" for k=0,...,dof-1.
> It's spelled VecStrideScale().
> > Same question for VecNorm: norm just an identified component?
> You guessed it, VecStrideNorm()

RIght!  Sorry to miss that.  Didn't search on "Stride".

> But, I actually recommend nondimensionalizing ... so that these component
> norms are not needed by the solvers, as the nondimensional system will
> generally produce a better conditioned algebraic system.

Did not need the norm for the solvers, actually.

I wrote a scaling/descaling "shell" around the residual evaluation
routine, so the latter could be dimensional.  At this early, prototype
stage, where I am at on my code, I don't want the "clutter" of
nondimensionalizing PDEs if I am familiar with them in dimensional

> ... nondimensionalizing (in the sense of ex48, not in terms on
> nondimensional numbers ...) ...

ex48.c is heavy-going if what one wants is an example showing how
PETSc can help with scaling the residual and Jacobian for better

Related question:  Is it true that an instance of DALocalFunction1
will cause trouble if it modifies the solution array?  (The values
supplied in the "Field *u" argument?)  It seems that this is so, which
I did not expect for this call-back.

Related comment:  There is no man page on DALocalFunction1, I think.



Ed Bueler
474-7693     (fax 474-5394)
Dept of Mathematics and Statistics
301C Chapman Hall, Univ of Alaska
Fairbanks, AK 99775-6660

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