DGESV_F90() -- Fortran90 wrapper to LAPACK DGESV

INTERFACE:

   SUBROUTINE DGESV_f90(A,B,IPIV,INFO)

USES:

      USE LA_PRECISION, ONLY: WP => DP
      USE LA_AUX, ONLY: ERINFO
      USE LAPACK77_INTERFACES, ONLY: GESV_F77 => DGESV
  
      IMPLICIT NONE

INPUT/OUTPUT PARAMETERS:

      REAL(WP), INTENT(INOUT) :: A(:,:), B(:,:)

OUTPUT PARAMETERS:

      INTEGER, INTENT(OUT), OPTIONAL :: INFO
      INTEGER, INTENT(OUT), OPTIONAL, TARGET :: IPIV(:)

DESCRIPTION:

This routine provides a Fortran90 wrapper to the LAPACK DGESV routine. Since it is written in Fortran90 it can determine numerous DGESV arguments at run-time, e.g., leading array dimensions from the arguments passed to the wrapper. Thus the wrapper has fewer arguments and is nicer to use.

The basic operation is a decomposition of the matrix A, i.e.,

where L is a left triangular matrix, and R is a right triangular matrix with 1's on the diagonal. In order to save space, A is overwritten.

DEFINED PARAMETERS:

      CHARACTER(LEN=7), PARAMETER :: SRNAME = 'LA_GESV'

LOCAL VARIABLES:

      INTEGER :: LD, LINFO, NRHS, N
      .. Local Pointers ..
      INTEGER, POINTER :: LPIV(:)

SYSTEM ROUTINES:

      INTRINSIC ALLOCATE, DEALLOCATE, MAX, PRESENT, SIZE
      INTRINSIC MAX, PRESENT, SIZE

BUGS:

      You have got to be kidding --- this is LAPACK90

REVISION HISTORY:

    12Feb97   Sawyer     Adaptation from LAPACK90 for this document

REMARKS:

      Anyone programming in Fortran90 should call this routine 
      and not the corresponding LAPACK DGESV routine.  It makes
      for much cleaner code.

CONTENTS:

      LINFO = 0
      N = SIZE(A, 1)
      IF( SIZE( A, 2 ) /= N ) THEN
         LINFO = -1
      ELSE IF( SIZE( B, 1 ) /= N ) THEN
         LINFO = -2
      ELSE
         IF( PRESENT( IPIV ) )THEN
            IF( SIZE( IPIV ) /= N ) LINFO = -3
         END IF
      END IF
!
      IF ( LINFO == 0 ) THEN
         LD = MAX( 1, N )
         NRHS = SIZE(B,2)
         IF( PRESENT( IPIV ) )THEN
            LPIV => IPIV
         ELSE
            ALLOCATE(LPIV(N))
         END IF
         CALL GESV_F77( N, NRHS, A, LD, LPIV, B, LD, LINFO )
         IF(.NOT.PRESENT(IPIV)) DEALLOCATE(LPIV)
      END IF
      CALL ERINFO(LINFO,SRNAME,INFO)