[petsc-users] function set by TSSetRHSJacobian() not being called

[Barry Smith]

   The Euler method is an explicit method that does not require the Jacobian. Hence the Jacobian you provide is never used.

    If you use any implement method, for example backward Euler beuler then you will see the Jacobian being used.

   Barry

> On Aug 9, 2016, at 2:08 PM, Scott Dossa <doss0032 at umn.edu> wrote:
> 
> Hi all,
> 
> I adapted ex13.c from .../ts/examples/tutorials/ex13.c to solve a 1D TD PDE (swift-hohenberg).
> Long story short: the function which sets the Jacobian is never being called despite being assigned by TSSetRHSJacobian().
> 
> I create the TS environment with the following commands (omitting some code before and after -- Full code attached):
> 
> ---------------------------------------------------------------------------------------------------------------------------------------------------------------------
>   ierr = DMDACreate1d(PETSC_COMM_WORLD, DM_BOUNDARY_NONE, 15, 1, 1, NULL, &da); CHKERRQ(ierr);
> 
>   /*==================================================================                                                                                                                                                                        
>     Let DMDA create vector                                                                                                                                                                                                                    
>     ==================================================================*/
> 
>   ierr = DMCreateGlobalVector(da, &x);CHKERRQ(ierr);
> 
>   /*==================================================================                                                                                                                                                                        
>     Create timestepper context which will use Euler Method                                                                                                                                                                                            
>     ==================================================================*/
> 
>   ierr = TSCreate(PETSC_COMM_WORLD,&ts);CHKERRQ(ierr);
>   ierr = TSSetDM(ts, da);CHKERRQ(ierr);
>   ierr = TSSetType(ts, TSEULER);CHKERRQ(ierr);
> 
>   ierr = TSSetRHSFunction(ts, x, RHSFunction, NULL);CHKERRQ(ierr);
> 
>   /*=================================================================                                                                                                                                                                         
>     Create Jacobian for Euler Method                                                                                                                                                                                                          
>     =================================================================*/
>   ierr = DMSetMatType(da, MATAIJ);CHKERRQ(ierr);
>   ierr = DMCreateMatrix(da,&J);CHKERRQ(ierr);
>   ierr = TSSetRHSJacobian(ts,J,J,RHSJacobian,NULL); CHKERRQ(ierr)
> ---------------------------------------------------------------------------------------------------------------------------------------------------------------------
> 
> I define the function RHSJacobian later, PetscPrintf(PETSC_COMM_WORLD, "Jacobian function called") is used to see if the function is ever called.
> 
> Neither is the message ever called, nor is the Jacobian matrix ever non-zero. The J matrix is checked with MatView( ). No error messages are produced either at compiling nor runtime.
> 
> Has anyone else run into such an issue or have any advice of how best to probe the problem? 
> Thanks so much!
> -Scott Dossa
> 
> 
> <swift.cpp>