C
C***********************************************************************
C                 COPYRIGHT ATLANTIC RICHFIELD COMPANY 1991            *
C***********************************************************************
CTITLESASYMIV -- PERFORM SYMMETRIC MATRIX INVERSE                       00010001
CA    AUTHOR       B. S. BOK                                            00030001
CA    DESIGNER     B. S. BOK                                            00040001
CA    LANGUAGE     FORTRAN                                              00050001
CA    SYSTEM       IBM / CRAY                                           00060004
CA    WRITTEN      AUGUST, 1990                                         00070001
C     REVISED      12-21-91 JJC - MODIFIED TO MEET EDP STANDARDS.
C
CA                                                                      00150001
CA    CALL SASYMIV (A, NN, N, B, IERR)
CA                                                                      00180000
CA         INPUT   A      = COLUMN-WISE INPUT ARRAY (SIZE OF NN)    R4  00190003
CA         INPUT   NN     = NO. OF DATA IN ARRAYS                   I4  00200003
CA         INPUT   N      = NO. OF COLUMNS OR ROWS                  I4  00210003
CA         OUTPUT  B      = COLUMN-WISE OUTPUT ARRAY (SIZE OF NN)   R4  00200003
CA         OUTPUT  IERR   = ERROR CODE (0 => NORMAL RETURN          I4  00210003
CA                                      9 => ABNORMAL RETURN )
CA                                                                      00350000
CA    THIS ROUTINE PERFORMS SYMMETRIC MATRIX INVERSE                    00360001
CA                                                                      00510000
C**************************************************************
C                                                             *
C SUBROUTINES AND FUNCTIONS CALLED FROM THIS ROUTINE          *
C                                                             *
C NO SUBROUTINES OR FUNCTIONS CALLED FROM THIS PROGRAM UNIT   *
C                                                             *
C**************************************************************
C
      SUBROUTINE SASYMIV(A, NN, N, B, IERR)
C
      IMPLICIT INTEGER (A-Z)
C
      DIMENSION A(1), B(1)
      DOUBLE PRECISION EK
C
      REAL     A
      REAL     B
      REAL     ZERO
C
      DATA ZERO  /1.0E-30/
C
C
      IERR = 0
      DO 100 I = 1, NN
         B(I) = 0.0
 100  CONTINUE
      IF (A(1) .GT. (-ZERO )  .AND. A(1) .LT. ZERO) THEN
         IERR = 9
         RETURN
      ENDIF
      B(1) = 1. / A(1)
      IF (NN .EQ. 1) RETURN
CC    DO 4 I = 2, NN
CC  4 B(I) = 0.
      MM = 1
      KN = 0
      DO 240 M = 2, N
         K = M - 1
         MM = MM + N + 1
         KN = KN + N
         EK = A(MM)
         MI = M - N
         DO 140 I = 1, K
            MI = MI + N
            IJ = I - N
            JM = KN
            DO 120 J = 1, K
               IJ = IJ + N
               JM = JM + 1
               EK = EK - A(MI) * B(IJ) * A(JM)
 120        CONTINUE
 140     CONTINUE
CC    B(MM) = 1./EK
         IF (EK .NE. 0.0) B(MM) = 1. / EK
         IF (EK .EQ. 0.0) B(MM) = 0.000
         MI = M - N
         IM = KN
         DO 180 I = 1, K
            IM = IM + 1
            IJ = I - N
            JM = KN
            DO 160 J = 1, K
               IJ = IJ + N
               JM = JM + 1
               B(IM) = B(IM) - B(IJ) * A(JM) * B(MM)
 160        CONTINUE
            MI = MI + N
            B(MI) = B(IM)
 180     CONTINUE
         IM = KN
         DO 220 I = 1, K
            IM = IM + 1
            MJ = M - N
            IJ = I - N
            DO 200 J = 1, K
               MJ = MJ + N
               IJ = IJ + N
               B(IJ) = B(IJ) + B(IM) * B(MJ) * EK
 200        CONTINUE
 220     CONTINUE
 240  CONTINUE
C
      RETURN
      END