1! 2! 3! Fortran kernel for sparse triangular solve in the AIJ matrix format 4! This ONLY works for factorizations in the NATURAL ORDERING, i.e. 5! with MatSolve_SeqAIJ_NaturalOrdering() 6! 7#include <petsc/finclude/petscsys.h> 8! 9pure subroutine FortranSolveAIJ(n,x,ai,aj,adiag,aa,b) 10 use, intrinsic :: ISO_C_binding 11 implicit none (type, external) 12 PetscScalar, intent(in) :: aa(0:*),b(0:*) 13 PetscInt, intent(in) :: n,ai(0:*), aj(0:*),adiag(0:*) 14 PetscScalar, intent(inout) :: x(0:*) 15 16 PetscInt i,jstart,jend 17 ! 18 ! Forward Solve 19 ! 20 x(0) = b(0) 21 do i=1,n-1 22 jstart = ai(i) 23 jend = adiag(i) - 1 24 x(i) = b(i) - sum(aa(jstart:jend)*x(aj(jstart:jend))) 25 end do 26 ! 27 ! Backward solve the upper triangular 28 ! 29 do i=n-1,0,-1 30 jstart = adiag(i) + 1 31 jend = ai(i+1) - 1 32 x(i) = x(i) - sum(aa(jstart:jend)*x(aj(jstart:jend))) * aa(adiag(i)) 33 end do 34end subroutine FortranSolveAIJ 35