*     F07JRF Example Program Text
*     Mark 21 Release. NAG Copyright 2004.
*     .. Parameters ..
      INTEGER          NIN, NOUT
      PARAMETER        (NIN=5,NOUT=6)
      INTEGER          NMAX
      PARAMETER        (NMAX=50)
*     .. Local Scalars ..
      INTEGER          I, INFO, N
*     .. Local Arrays ..
      COMPLEX *16      E(NMAX-1)
      DOUBLE PRECISION D(NMAX)
*     .. External Subroutines ..
      EXTERNAL         ZPTTRF
*     .. Executable Statements ..
      WRITE (NOUT,*) 'F07JRF Example Program Results'
      WRITE (NOUT,*)
*     Skip heading in data file
      READ (NIN,*)
      READ (NIN,*) N
      IF (N.LE.NMAX) THEN
*
*        Read the lower bidiagonal part of the tridiagonal matrix A from
*        data file
*
         READ (NIN,*) (D(I),I=1,N)
         READ (NIN,*) (E(I),I=1,N-1)
*
*        Factorize the tridiagonal matrix A
*
         CALL ZPTTRF(N,D,E,INFO)
*
         IF (INFO.GT.0) THEN
            WRITE (NOUT,99999) 'The leading minor of order ', INFO,
     +        ' is not positive definite'
         END IF
*
*        Print details of the factorization
*
         WRITE (NOUT,*) 'Details of factorization'
         WRITE (NOUT,*)
         WRITE (NOUT,*) ' The diagonal elements of D'
         WRITE (NOUT,99998) (D(I),I=1,N)
         WRITE (NOUT,*)
         WRITE (NOUT,*)
     +     ' Sub-diagonal elements of the Cholesky factor L'
         WRITE (NOUT,99998) (E(I),I=1,N-1)
*
      ELSE
         WRITE (NOUT,*) 'NMAX too small'
      END IF
*
99999 FORMAT (1X,A,I3,A)
99998 FORMAT (1X,8F9.4)
      END