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    1:       SUBROUTINE ZPTSV( N, NRHS, D, E, B, LDB, INFO )
    2: *
    3: *  -- LAPACK routine (version 3.2) --
    4: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
    5: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
    6: *     November 2006
    7: *
    8: *     .. Scalar Arguments ..
    9:       INTEGER            INFO, LDB, N, NRHS
   10: *     ..
   11: *     .. Array Arguments ..
   12:       DOUBLE PRECISION   D( * )
   13:       COMPLEX*16         B( LDB, * ), E( * )
   14: *     ..
   15: *
   16: *  Purpose
   17: *  =======
   18: *
   19: *  ZPTSV computes the solution to a complex system of linear equations
   20: *  A*X = B, where A is an N-by-N Hermitian positive definite tridiagonal
   21: *  matrix, and X and B are N-by-NRHS matrices.
   22: *
   23: *  A is factored as A = L*D*L**H, and the factored form of A is then
   24: *  used to solve the system of equations.
   25: *
   26: *  Arguments
   27: *  =========
   28: *
   29: *  N       (input) INTEGER
   30: *          The order of the matrix A.  N >= 0.
   31: *
   32: *  NRHS    (input) INTEGER
   33: *          The number of right hand sides, i.e., the number of columns
   34: *          of the matrix B.  NRHS >= 0.
   35: *
   36: *  D       (input/output) DOUBLE PRECISION array, dimension (N)
   37: *          On entry, the n diagonal elements of the tridiagonal matrix
   38: *          A.  On exit, the n diagonal elements of the diagonal matrix
   39: *          D from the factorization A = L*D*L**H.
   40: *
   41: *  E       (input/output) COMPLEX*16 array, dimension (N-1)
   42: *          On entry, the (n-1) subdiagonal elements of the tridiagonal
   43: *          matrix A.  On exit, the (n-1) subdiagonal elements of the
   44: *          unit bidiagonal factor L from the L*D*L**H factorization of
   45: *          A.  E can also be regarded as the superdiagonal of the unit
   46: *          bidiagonal factor U from the U**H*D*U factorization of A.
   47: *
   48: *  B       (input/output) COMPLEX*16 array, dimension (LDB,N)
   49: *          On entry, the N-by-NRHS right hand side matrix B.
   50: *          On exit, if INFO = 0, the N-by-NRHS solution matrix X.
   51: *
   52: *  LDB     (input) INTEGER
   53: *          The leading dimension of the array B.  LDB >= max(1,N).
   54: *
   55: *  INFO    (output) INTEGER
   56: *          = 0:  successful exit
   57: *          < 0:  if INFO = -i, the i-th argument had an illegal value
   58: *          > 0:  if INFO = i, the leading minor of order i is not
   59: *                positive definite, and the solution has not been
   60: *                computed.  The factorization has not been completed
   61: *                unless i = N.
   62: *
   63: *  =====================================================================
   64: *
   65: *     .. External Subroutines ..
   66:       EXTERNAL           XERBLA, ZPTTRF, ZPTTRS
   67: *     ..
   68: *     .. Intrinsic Functions ..
   69:       INTRINSIC          MAX
   70: *     ..
   71: *     .. Executable Statements ..
   72: *
   73: *     Test the input parameters.
   74: *
   75:       INFO = 0
   76:       IF( N.LT.0 ) THEN
   77:          INFO = -1
   78:       ELSE IF( NRHS.LT.0 ) THEN
   79:          INFO = -2
   80:       ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
   81:          INFO = -6
   82:       END IF
   83:       IF( INFO.NE.0 ) THEN
   84:          CALL XERBLA( 'ZPTSV ', -INFO )
   85:          RETURN
   86:       END IF
   87: *
   88: *     Compute the L*D*L' (or U'*D*U) factorization of A.
   89: *
   90:       CALL ZPTTRF( N, D, E, INFO )
   91:       IF( INFO.EQ.0 ) THEN
   92: *
   93: *        Solve the system A*X = B, overwriting B with X.
   94: *
   95:          CALL ZPTTRS( 'Lower', N, NRHS, D, E, B, LDB, INFO )
   96:       END IF
   97:       RETURN
   98: *
   99: *     End of ZPTSV
  100: *
  101:       END