[petsc-users] TS with inhomogeneous rhs

[Barry Smith]

  For this we recommend using petsc-dev http://www.mcs.anl.gov/petsc/petsc-as/developers/index.html and using TSSetIFunction() and TSSetIJacobian().

   We are transistioning to use this new interface for everything because it handles more general situations than the old interfaces.

   Barry


On Nov 18, 2010, at 4:14 PM, Chetan Jhurani wrote:

> Hello,
> 
> Question in brief:  what's a good way, using TS, to solve a system of
> ODEs which looks like this?
> 
> 	M U_t = -K U + f(t)
> 
> In addition, how can the code be kept nearly identical to allow different
> TS types to be used (EULER, BEULER, TSRUNGE_KUTTA, TSCRANK_NICHOLSON,
> etc)?  I'd also like to take possible advantages of M and K being
> constants.
> 
> Background and what I've tried:
> 
> If f(t) were not present TSSetMatrices seems like the convenient
> way ahead.  In fact, I can still use the same function in presence of
> f(t) for an explicit time-stepping method like RK or Euler if I use
> a MatShell for Arhs, and sneak in f(t) there.
> 
> But I cannot use an implicit method like Backward Euler with a
> MatShell for Arhs easily.  It needs MatFactor to be implemented
> for the shell matrix (at least).
> 
> Is there something I'm missing?  This is a common system of equation.
> 
> Most TS examples solve u_t = u_xx, convenient for TSSetMatrices.
> 
> ts/examples/tests/ex3.c looks like it should work for a system
> with f(t).  But it needs the Jacobian matrix of RHS and it evaluates
> it using finite differences.  In addition, for each time-step it
> computes an ILU factorization.
> 
> Thanks,
> 
> Chetan
> 
> 
>