[petsc-users] TS with inhomogeneous rhs

[Chetan Jhurani]

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