[petsc-users] Problem with SNES

[Jed Brown]

On Sat, Aug 27, 2011 at 13:04, Milan Mitrovic <milan.v.mitrovic at gmail.com>wrote:

> well... I added matrix elements by row (~150 nonzero elements) but I
> have 7.5k rows per processor... I know the exact nonzero pattern and I
> preallocated the storage so it is not that... and its all done
> locally... I couldn't insert blocks because there is no common
> structure to the nonzero pattern of different rows...
>
> so to me it seems that creating the matrix like this should be fast...
> computing the values took <3 seconds but the setvalues routine took
> more than a minute!
>

Preallocation must have been wrong. Perhaps it was destroyed/ignored by
calling the function too early (the matrix type has to be set _before_
preallocation). Try
MatSetOption(A,MAT_NEW_NONZERO_ALLOCATION_ERR,PETSC_TRUE) and run in a
debugger to see where new entries are being allocated. With petsc-dev, you
can just run with -mat_new_nonzero_allocation_err.
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