preconditioning.f File Reference

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Functions/Subroutines
subroutine	preconditioning (ad, au, b, neq, irow, jq, adaux)

Function/Subroutine Documentation

preconditioning()

subroutine preconditioning	(	real*8, dimension(*), intent(inout)	ad,
		real*8, dimension(*), intent(inout)	au,
		real*8, dimension(*), intent(inout)	b,
		integer, intent(in)	neq,
		integer, dimension(*), intent(in)	irow,
		integer, dimension(*), intent(in)	jq,
		real*8, dimension(*), intent(inout)	adaux
	)

!
      implicit none
!
      integer neq,irow(*),jq(*),i,ic,ir
!
      real*8 ad(*),au(*),b(*),adaux(*),adc
!
      intent(in) neq,irow,jq
!
      intent(inout) ad,au,b,adaux
!
!     inverse of the square root of the diagonal
!     the sign takes care that the diagonal term becomes 1 
!     (and not -1)
!
      do i=1,neq
         adaux(i)=dsign(1.d0/dsqrt(dabs(ad(i))),ad(i))
      enddo
c      do i=1,neq
c         adaux(i)=1.d0/dsqrt(dabs(ad(i)))
c      enddo
!
!     scaling the matrix and the right hand side
!
      do ic=1,neq
         adc=dabs(adaux(ic))
!
!        scaling the diagonal
!
         ad(ic)=ad(ic)*adc*adaux(ic)
!
!        scaling the off-diagonal terms
!
         do i=jq(ic),jq(ic+1)-1
            ir=irow(i)
            au(i)=au(i)*adc*adaux(ir)
         enddo
!
!        scaling the right hand side
!
         b(ic)=b(ic)*adaux(ic)
      enddo
!
!     taking the absolute value
!
      do i=1,neq
         adaux(i)=dabs(adaux(i))
      enddo
!
      return