[petsc-users] from standard fortran program to PETSc

[Anthony Paul Haas]

Hi Satish,

Thanks for your answer. In the attached program, I have declared the
following standard fortran arrays: real(dp),dimension(:,:),allocatable ::
D1X,D2X,D1Y,D2Y
Let's say these are real matrix derivatives that I need to insert in my
complex A matrix (it could also be some real baseflow from a similarity
solver). I have filled D1Y with 999.d0 just to test (see line 169). Then I
insert D1Y in the global (complex) matrix with call
MatSetValues(A,ny,idxm2,ny,idxn2,D1Y,INSERT_VALUES,ierr). I expected that
in the Matrix A, this would be automatically converted to 999.0 + 0.0i but
when I view A, I see 999 + 999 i or even 999 + 1.0326e-321 i. Is there a
way to insert D1Y as is and obtain the proper behavior? How would you do it?

Thanks

Anthony

On Fri, Jun 19, 2015 at 11:08 AM, Satish Balay <balay at mcs.anl.gov> wrote:

> On Fri, 19 Jun 2015, Anthony Haas wrote:
>
> > Hi,
> >
> > I have a Fortran90 program that solves a complex linear generalized
> eigenvalue
> > problem (GEVP) using standard fortran 90 programming:
> >
> > Subroutines, modules, allocatable arrays, real(8), int,...
> >
> > This program uses Lapack to solve the GEVP. The program is mainly made
> off:
> >
> > 1) set dimensions of problem and initialize arrays,...
> > 2) compute the baseflow (for instance boundary layer flow)
> > 3) build the (stability) complex generalized eigenvalue problem ==> build
> > (dense) matrices A and B
> > 4) solve the GEVP with Lapack
> >
> > Now I want to use PETSc + SLEPc to use sparse matrices. Do I need to
> > rewrite/modify everything in terms of PETSc variables as follows:
> >
> > - int -> PetscInt
> > - real(8) -> PetscScalar
> perhaps you mean: PetscReal
>
> > - complex*16 -> PetscScalar
> >
> > or is it possible to reuse all that F90 code? For instance I have a
> similarity
> > solver that computes Blasius solution. If that similarity solver
> provides me
> > with u and v velocities in terms of standard fortran90 real(8)
> variables, how
> > should I do to use these variables to build my complex matrix? Should I
> > convert them to Petsc variables? How?
> >
>
> You can use the current datatypes used in your code - And always make
> sure the types match manually. [Fortran does not have typecheck anyway..]
>
> > what should I do with my Fortran90 allocatable arrays?
> >
> > real(dp),allocatable,dimension(:,:) :: u-->
> > PetscScalar,allocatable,dimension(:,:) :: u ????
>
> Either should work.
>
> You can add the following to your code:
>
> #if !defined(PETSC_USE_COMPLEX)
> #error "this code requires PETSc --with-scalar-type=complex build"
> #endif
> #if !defined(PETSC_USE_REAL_DOUBLE)
> #error "this code requires PETSc --with-precision=real build"
> #endif
>
> Satish
>
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