message: explicitly call TSSetEquationType and TSSetProblemType
diff: @@ -2780,6 +2780,11 @@ void PetscODESolver::Init(TimeDependentOperator &f_,
  }
  if (!f_.isHomogeneous())
  {
  + if (!f_.isImplicit())
  + {
  + ierr = TSSetEquationType(ts, TS_EQ_EXPLICIT);
  + PCHKERRQ(ts, ierr);
  + }
  ierr = TSSetRHSFunction(ts, NULL, __mfem_ts_rhsfunction, (void *)ts_ctx);
  PCHKERRQ(ts, ierr);
  ierr = TSSetRHSJacobian(ts, NULL, NULL, __mfem_ts_rhsjacobian, (void *)ts_ctx);
  @@ -2792,6 +2797,11 @@ void PetscODESolver::Init(TimeDependentOperator &f_,
  ts_ctx->cached_shift = std::numeric_limits<PetscReal>::min();
  ts_ctx->type = type;
  ts_ctx->computed_rhsjac = false;
  + if (type == ODE_SOLVER_LINEAR)
  + {
  + ierr = TSSetProblemType(ts, TS_LINEAR);
  + PCHKERRQ(ts, ierr);
  + }
  }
  void PetscODESolver::SetJacobianType(Operator::Type jacType)
  