[petsc-users] MPI v. Pthreads ?

[Jed Brown]

On Sun, Jul 10, 2011 at 05:44, John Chludzinski <jchludzinski at gmail.com>wrote:

> 2) Since threads can share data (variables), wouldn't there be less of a
> need to send/receive data than using MPI, which simply spawns separate
> disjoint processes?
>

Yes, threads allow more things to be shared, but there is still a problem of
data locality and it is often faster to copy than to share.


>
> 3) "  Vec and Mat class"?  I hope you're sticking with C (v. C++)?  I've
> used G++ version 4.3.4 and version 4.5.2 and got different answers with the
> exact same source.  I have used Visual C++ (2008) and got different answers
> than G++ 4.6.1 - again the same source.  C99 seems to give consistent
> results across compilers/platforms and is simpler to boot.
>

We generally prefer C to C++, but the symptoms you describe are likely to be
caused by writing code with undefined behavior. Unfortunately, there is no
checker for undefined behavior, but compiling with -std=c++98 -Wall -Wextra
-pedantic does show many things.
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