[petsc-users] ERROR: Cannot pass default in for both input and output indices

[Jed Brown]

On Mon, Oct 24, 2011 at 15:29, Dominik Szczerba <dominik at itis.ethz.ch>wrote:

> ierr = ISGetLocalSize(ix,&nx);CHKERRQ(ierr);
> ...
> ierr = ISGetLocalSize(iy,&ny);CHKERRQ(ierr);
> ...
> if (nx != ny) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_SIZ,"Local scatter
> sizes don't match");
>
>
>
> which looks quite suspicious to me, i.e. 1) If iy is PETSC_NULL, how
> can its size be queried?
>

Your confusion comes from not looking at the earlier part of the function
where index sets are created if you passed in NULL. The only reason ix=NULL
and iy=NULL is not allowed is that it's a rare case that more frequently
represents misunderstanding. If it's really what you want, then just make
the index set.
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