[petsc-users] from standard fortran program to PETSc

[Satish Balay]

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