Re: [petsc-users] DMDAVecGetArray

[anton]

On 04/23/2015 01:36 PM, Matthew Knepley wrote:
On Thu, Apr 23, 2015 at 6:28 AM, anton <po...@uni-mainz.de 
<mailto:po...@uni-mainz.de>> wrote:

    Hi,

    I'm currently calling DMDAVecGet(Restore)Array on a subset of
    processors. It seems to work correctly. So why does documentation
    say they are collective on Vec? Are they really? Unlike VecNorm,
    for example, it's not really clear why DMDAVecGetArray should be
    collective.


The documentation should be fixed. Its "logically collective" just 
like VecGetArray(), and unlike VecGetArrayRead().

    Am I still on a safe side, or I'm seriously violating something
    that's not immediately obvious.


You are violating something that is not obvious. GetArray() will 
increment the status marker on the Vec since you
could have changed something, but then you will get inconsistency 
across processes in this marker, so you could
make different decisions about whether to recompute norms, etc. Hard 
to debug errors.


OK, thanks Matt, I'll simply add dummy calls on those processes where I 
don't need the data.

Anton

  Thanks,

     Matt

    Thanks,
    Anton




--
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