[petsc-users] DM and HDF5 Viewer

[Barry Smith]

> On Jul 16, 2015, at 11:14 AM, Jed Brown <jed at jedbrown.org> wrote:
> 
> Gianluca Meneghello <gianmail at gmail.com> writes:
> 
>> Hi again,
>> 
>> I am now trying to write a vector to an HDF5, this time using a DM
>> structure to impose the vector layout.
>> 
>> Creating the vector with (as in src/dm/examples/tutorials/ex10.c)
>> 
>> DMCreateGlobalVector(da2D,&gauss);
>> 
>> every works fine, i.e. the hdf5 file has the correct layout given by the
>> dimension of the DM. On the other side, if I use:
>> 
>> VecCreate(PETSC_COMM_WORLD,&gauss);
>> VecSetSizes(gauss,PETSC_DECIDE,Nx*Ny);
>> VecSetDM(gauss,da2D);
> 
> VecSetDM only associates a DM with the Vec.  It does not interpose
> itself into VecView.
> 
> Should we change this so that creating a Vec of the correct size/block
> size/layout and associating a DM is equivalent?  Perhaps, but it's more
> nuanced than it might seem.

  Yikes. VecSetDM() seems a very dangerous and odd thing. Should it exist? If it exists it seems it should be exactly equivalent to creating the vector from the DM.

> 
> Why don't you want to just call DMCreateGlobalVector()?