[petsc-users] Does an array obtained with VecGetArray remain valid after vec's values changed?

[Satish Balay]

On Mon, 31 Oct 2011, Dominik Szczerba wrote:

> In the documentation of VecGetArray I read that it returns a pointer
> to the local data array and does not use any copies. Does this mean,
> that changing the values of the vector followed by
> VecAssemblyBegin/End does NOT invalidate the pointer? In other words,
> do I need to re-get the array when vec's values are changed?

For one - you don't need VecAssemblyBegin/End if you obtain the array
with VecGetArray() - and change values there.

Also - after you are done using the array - you should call
VecRestoreArray().  And you should be changing the values only between
these two calls. [i.e do not stash the pointer for later use - and
keep changing values with this pointer - after the call to
VecRestroeArray()].  If you need to change the vec again - call
VecGetArray() again.


Note: With VecGetArray() - you get access to local array - so can
modify only local values. If you have to set values that might go to a
different processor - then VecSetValues() - with
VecAssemblyBegin/End() - is the correct thing to do.

Satish