[petsc-users] cached values

[Justin Chang]

Okay that makes a lot of sense, I was confused because I thought the word
cache referred to computer hardware caches. Thanks everyone for your input

On Sun, Apr 26, 2015 at 8:58 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>   The word cache here is not directly related to computer hardware caches.
> It comes from the meaning "store away in hiding or for future use." We also
> use the term stash "store (something) safely and secretly in a specified
> place". It is used to mean store temporarily (out of sight or knowledge)
> until we build the final matrix/vector  data structure.  For example if one
> sets a value into a matrix on one process that actually belongs on a
> different process we "stash it away" until the MatAssemblyBegin/End() when
> we move the data to the correct process and put it into its final resting
> place". As Patrick notes sometimes you may even want to stash values that
> that will eventually be stored locally.
>
>   Barry
>
>   The reason we use stash or cache with the "secret or hiding" status is
> that once the values are stashed the user doesn't have direct access to
> them at that time, it is only after the MatAssemblyBegin/End that you get
> that direct access again.
>
>
> > On Apr 26, 2015, at 6:49 PM, Justin Chang <jychang48 at gmail.com> wrote:
> >
> > Hello everyone,
> >
> > Pardon me if this might be a PETSc 101 question, but what exactly is
> meant when routines like MatSetValues() "caches the values"? Specifically,
> what happens say, after I iterate through each element within the
> ComputeJacobian() routine, when I call MatAssemblyBegin/End(). If there's
> documentation or a paper somewhere that explains this that would be very
> helpful, because I can't seem to find anything in the PETSc manual
> describing this process in detail.
> >
> > Thanks,
> > Justin
>
>
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