[petsc-users] Error in vec/vec/examples/tutorials/ex19.c

[Sajid Ali]

I thought I fixed it by using VecDuplicate instead of setting up x2 &
copying but I got more confused as to why the VecWrite had different
dimensions in each case.

Does blocking take a Nx1 vector and convert it to N/BLOCK_SIZE x BLOCK_SIZE
vector (that's how it looked it in the output hdf5 files) ?

Since I didn't find TimeStep to be a feature of HDF5, am I right in
assuming that it's a PETSc feature that creates an extra dimension to store
multiple vectors (with the new dimension being indexed by
PetscViewerHDF5SetTimeStep) ?

On Fri, Nov 30, 2018 at 5:17 PM Smith, Barry F. <bsmith at mcs.anl.gov> wrote:

>
>
> > On Nov 30, 2018, at 1:30 PM, Sajid Ali via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
> >
> > Hi,
> >
> > I tried running ex19.c and I get the following error (I added a small
> snippet to print the local size on rank0 as well) :
> >
> > [sajid at xrm temp]$ mpirun -np 2 ./ex19
> > local_sizes : 3 4
> > [1]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> > [1]PETSC ERROR: Arguments are incompatible
> > [1]PETSC ERROR: Incompatible vector local lengths parameter # 1 local
> size 3 != parameter # 2 local size 2
> > [1]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
> > [1]PETSC ERROR: Petsc Release Version 3.10.2, unknown
> > [1]PETSC ERROR: ./ex19 on a  named xrm by sajid Fri Nov 30 13:28:36 2018
> > [1]PETSC ERROR: [0]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> > [0]PETSC ERROR: Arguments are incompatible
> > [0]PETSC ERROR: Incompatible vector local lengths parameter # 1 local
> size 3 != parameter # 2 local size 4
> > [0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
> > [0]PETSC ERROR: Petsc Release Version 3.10.2, unknown
> > [0]PETSC ERROR: ./ex19 on a  named xrm by sajid Fri Nov 30 13:28:36 2018
> >
> > Does this mean that PETSC_DECIDE is inconsistent between two calls in
> the same file ?
>
>    No. The reason for the error is a bug in the code. The x1 vector has a
> block size of 1 hence when it is divided among two processes it gets 3
> entries on each process. The x2 vector has a block size of 2 so when it is
> divided among two processes it gets 4 entries on the first process and 2 on
> the second. The call to VecCopy() does not work because the two vectors
> have different layouts.
>
>    I have attached a fixed version of the code (that does not copy from x1
> to x2).
>
>      Barry
>
>
>
> >
> > Thank You,
> > Sajid Ali
> > Applied Physics
> > Northwestern University
>
>

-- 
Sajid Ali
Applied Physics
Northwestern University
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