invert.f

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!                       *****************
                        SUBROUTINE invert
!                       *****************
!
     &( rn    , n     , np    )
!
!***********************************************************************
! TOMAWAC   V6P2                                   25/06/2012
!***********************************************************************
!
!brief    CALCULATION OF INVERSE MATRIX NXN
!+
!+            TAKEN FROM NUMERICAL RECEIPES IN FORTRAN 77
!+            USED IN THE FREE-MESH METHOD (DIFFRACTION)
!
!history  E. KRIEZI (LNH)
!+        04/12/2006
!+        V5P5
!+
!
!
!history  G.MATTAROLO (EDF - LNHE)
!+        23/06/2012
!+        V6P2
!+        Modification for V6P2
!
!~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
!| N              |-->| MATRIX DIMENSION
!| NP             |-->| MATRIX PHYSICAL DIMENSION
!| RN             |<->| MATRIX TO INVERT
!~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
!
      USE interface_tomawac, ex_invert => invert
      IMPLICIT NONE
!
!.....VARIABLES IN ARGUMENT
!     """"""""""""""""""""
      INTEGER, INTENT(IN) :: N, NP
      DOUBLE PRECISION, INTENT(INOUT) :: RN(np,np)
!
!.....LOCAL VARIABLES
!     """""""""""""""
      INTEGER INDX(np),I,J
      DOUBLE PRECISION Y(np,np), A(np,np)
!~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
!
      a=rn
      DO i=1,n
        DO j=1,n
          y(i,j)=0.
        ENDDO
        y(i,i)=1.
      ENDDO
      CALL ludcmp(a,n,np,indx)
      DO j=1,n
        CALL lubksb(a,n,np,indx,y(1,j))
      ENDDO
      rn=y
!
      RETURN
      END