SUBROUTINE SPTSL(N,D,E,B)
      INTEGER N
      REAL D(1),E(1),B(1)
C
C     SPTSL GIVEN A POSITIVE DEFINITE TRIDIAGONAL MATRIX AND A RIGHT
C     HAND SIDE WILL FIND THE SOLUTION.
C
C     ON ENTRY
C
C        N        INTEGER
C                 IS THE ORDER OF THE TRIDIAGONAL MATRIX.
C
C        D        REAL(N)
C                 IS THE DIAGONAL OF THE TRIDIAGONAL MATRIX.
C                 ON OUTPUT D IS DESTROYED.
C
C        E        REAL(N)
C                 IS THE OFFDIAGONAL OF THE TRIDIAGONAL MATRIX.
C                 E(1) THROUGH E(N-1) SHOULD CONTAIN THE
C                 OFFDIAGONAL.
C
C        B        REAL(N)
C                 IS THE RIGHT HAND SIDE VECTOR.
C
C     ON RETURN
C
C        B        CONTAINS THE SOULTION.
C
C     LINPACK. THIS VERSION DATED 08/14/78 .
C     JACK DONGARRA, ARGONNE NATIONAL LABORATORY.
C
C     NO EXTERNALS
C     FORTRAN MOD
C
C     INTERNAL VARIABLES
C
      INTEGER K,KBM1,KE,KF,KP1,NM1,NM1D2
      REAL T1,T2
C
C     CHECK FOR 1 X 1 CASE
C
      IF (N .NE. 1) GO TO 10
         B(1) = B(1)/D(1)
      GO TO 70
   10 CONTINUE
         NM1 = N - 1
         NM1D2 = NM1/2
         IF (N .EQ. 2) GO TO 30
            KBM1 = N - 1
C
C           ZERO TOP HALF OF SUBDIAGONAL AND BOTTOM HALF OF
C           SUPERDIAGONAL
C
            DO 20 K = 1, NM1D2
               T1 = E(K)/D(K)
               D(K+1) = D(K+1) - T1*E(K)
               B(K+1) = B(K+1) - T1*B(K)
               T2 = E(KBM1)/D(KBM1+1)
               D(KBM1) = D(KBM1) - T2*E(KBM1)
               B(KBM1) = B(KBM1) - T2*B(KBM1+1)
               KBM1 = KBM1 - 1
   20       CONTINUE
   30    CONTINUE
         KP1 = NM1D2 + 1
C
C        CLEAN UP FOR POSSIBLE 2 X 2 BLOCK AT CENTER
C
         IF (MOD(N,2) .NE. 0) GO TO 40
            T1 = E(KP1)/D(KP1)
            D(KP1+1) = D(KP1+1) - T1*E(KP1)
            B(KP1+1) = B(KP1+1) - T1*B(KP1)
            KP1 = KP1 + 1
   40    CONTINUE
C
C        BACK SOLVE STARTING AT THE CENTER, GOING TOWARDS THE TOP
C        AND BOTTOM
C
         B(KP1) = B(KP1)/D(KP1)
         IF (N .EQ. 2) GO TO 60
            K = KP1 - 1
            KE = KP1 + NM1D2 - 1
            DO 50 KF = KP1, KE
               B(K) = (B(K) - E(K)*B(K+1))/D(K)
               B(KF+1) = (B(KF+1) - E(KF)*B(KF))/D(KF+1)
               K = K - 1
   50       CONTINUE
   60    CONTINUE
         IF (MOD(N,2) .EQ. 0) B(1) = (B(1) - E(1)*B(2))/D(1)
   70 CONTINUE
      RETURN
      END