KLU sparse solver and SPGMR preconditioning for IDA solver

I am trying to pass Jacobian as a sparse matrix through a jac function for the IDA solver. However, the code only take two types of linear solvers i.e. dense or SPGMR.

I understand it requires the interface for sparse KLU solver library in IDA which is not yet implemented in Assimulo. So, I proceeded with the SPGMR solver to pass a preconditioned matrix as per SUNDIALS documentation.

In the Assimulo documentation examples, I could find an example (ida_with_jac_spgmr.py) where jacv (Jacobian times vector) function is implemented. In this example, I figured there is no preconditioning used. Then looked at another example in CVODE (Explicit_Problem) where preconditioning is used (cvode_with_preconditioning.py).

However, trying out the same structure for IDA (Implicit_Problem) didn't work. The error was, the options for preconditioning were not available for IDA solver. I came to a conclusion about the behavior of this by looking into the source code of sundials.pyx.

---------------------------------Snippet of source code-------------------------------------------------------------------------

# From [sundials.pyx file](https://github.com/modelon-community/Assimulo/blob/master/src/solvers/sundials.pyx)---provides only two solvers-DENSE/SPGMR
if self.options["linear_solver"] == 'DENSE':

elif self.options["linear_solver"] == 'SPGMR':
    # PREC_NONE implies no preconditioner option is supplied to SUNDIALS
    IF SUNDIALS_VERSION >= (3,0,0):
        #Create the linear solver
        IF SUNDIALS_VERSION >= (4,0,0):
            IF SUNDIALS_VERSION >= (6,0,0):
                self.sun_linearsolver = SUNDIALS.SUNLinSol_SPGMR(self.yTemp, **PREC_NONE**, 0, ctx)
            ELSE:
                self.sun_linearsolver = SUNDIALS.SUNLinSol_SPGMR(self.yTemp, **PREC_NONE**, 0)
        ELSE:
            self.sun_linearsolver = SUNDIALS.SUNSPGMR(self.yTemp, PREC_NONE, 0)

        #Attach it to IDAS
        IF SUNDIALS_VERSION >= (4,0,0):
            flag = SUNDIALS.IDASetLinearSolver(self.ida_mem, self.sun_linearsolver, NULL)
        ELSE:
            flag = SUNDIALS.IDASpilsSetLinearSolver(self.ida_mem, self.sun_linearsolver)

From the comments I added in the code snippet from the source code, I understood that the preconditioning functionality for the SPGMR solver is not exposed in sundials.pyx file.

Let me know if I my understanding is correct. If yes, is there a chance for this functionality to be exposed? It would be really helpful if you could provide some information on this.

modelon-community / Assimulo

KLU sparse solver and SPGMR preconditioning for IDA solver #86