[petsc-dev] Errors with DM & PCSHELL

[Barry Smith]

> On May 29, 2015, at 10:32 AM, Mark Adams <mfadams at lbl.gov> wrote:
> 
> I am getting errors in code that I thought was working ...
> 
> I create a PC shell like so:
> 
>   ! set shell PC
>   call SNESGetKSP(solver%snes,innerksp,ierr)
>   call KSPGetPC(innerksp,spc,ierr)  
>   call PCSetType(spc,PCSHELL,ierr) ! overriding opions !!!
>   call PCShellSetApply(spc,PCShermanMorrisonApply,ierr)
>   call PCSetApplicationContext(spc,solver,ierr)
> 
> and in PCShermanMorrisonApply I have:
> 
>   call PCGetApplicationContext(pc,solver,ierr)
>   call DMCompositeGetAccessArray(solver%da,xin,itwo,PETSC_NULL_INTEGER,Xsub,ierr)
>   call DMCompositeGetAccessArray(solver%da,yout,itwo,PETSC_NULL_INTEGER,Ysub,ierr)
>   call PCFieldSplitGetSubKSP(solver%pc,PETSC_NULL_INTEGER,subksp,ierr)
>   call KSPSolve(subksp(1),Xsub(1),Ysub(1),ierr)
>   call MatMult(solver%Cmat,Ysub(1),Xsub(2),ierr) ! ignoring <> input
> 
> I get an error on this last statement about a vector being locked.

   What vector? the Xsub(2) vector? 

   Based on the names of the variable I am guessing that xin is the input vector to your Apply() hence it is read only. Thus Xsub is read only, but you are trying to put the results of a MatMult() int Xsub(2) which is completely wrong. You cannot use Xsub for work space because it will corrupt the outer solver.

>  There does not seem to be:
> 
> call DMCompositeGetAccessArrayRead( ...

   There doesn't need to be. Internally the DMCompositeGetAccessArray() will make the subvectors read only if the large vector is read only. 

> 
> I thought I fixed this problem ... or at least one like it.
> 
> Mark