zptsv.f

          SUBROUTINE ZPTSV( N, NRHS, D, E, B, LDB, INFO )
    *
    *  -- LAPACK routine (version 3.1) --
    *     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
    *     November 2006
    *
    *     .. Scalar Arguments ..
          INTEGER            INFO, LDB, N, NRHS
    *     ..
    *     .. Array Arguments ..
          DOUBLE PRECISION   D( * )
          COMPLEX*16         B( LDB, * ), E( * )
    *     ..
    *
    *  Purpose
    *  =======
    *
    *  ZPTSV computes the solution to a complex system of linear equations
    *  A*X = B, where A is an N-by-N Hermitian positive definite tridiagonal
    *  matrix, and X and B are N-by-NRHS matrices.
    *
    *  A is factored as A = L*D*L**H, and the factored form of A is then
    *  used to solve the system of equations.
    *
    *  Arguments
    *  =========
    *
    *  N       (input) INTEGER
    *          The order of the matrix A.  N >= 0.
    *
    *  NRHS    (input) INTEGER
    *          The number of right hand sides, i.e., the number of columns
    *          of the matrix B.  NRHS >= 0.
    *
    *  D       (input/output) DOUBLE PRECISION array, dimension (N)
    *          On entry, the n diagonal elements of the tridiagonal matrix
    *          A.  On exit, the n diagonal elements of the diagonal matrix
    *          D from the factorization A = L*D*L**H.
    *
    *  E       (input/output) COMPLEX*16 array, dimension (N-1)
    *          On entry, the (n-1) subdiagonal elements of the tridiagonal
    *          matrix A.  On exit, the (n-1) subdiagonal elements of the
    *          unit bidiagonal factor L from the L*D*L**H factorization of
    *          A.  E can also be regarded as the superdiagonal of the unit
    *          bidiagonal factor U from the U**H*D*U factorization of A.
    *
    *  B       (input/output) COMPLEX*16 array, dimension (LDB,N)
    *          On entry, the N-by-NRHS right hand side matrix B.
    *          On exit, if INFO = 0, the N-by-NRHS solution matrix X.
    *
    *  LDB     (input) INTEGER
    *          The leading dimension of the array B.  LDB >= max(1,N).
    *
    *  INFO    (output) INTEGER
    *          = 0:  successful exit
    *          < 0:  if INFO = -i, the i-th argument had an illegal value
    *          > 0:  if INFO = i, the leading minor of order i is not
    *                positive definite, and the solution has not been
    *                computed.  The factorization has not been completed
    *                unless i = N.
    *
    *  =====================================================================
    *
    *     .. External Subroutines ..
          EXTERNAL           XERBLA, ZPTTRF, ZPTTRS
    *     ..
    *     .. Intrinsic Functions ..
          INTRINSIC          MAX
    *     ..
    *     .. Executable Statements ..
    *
    *     Test the input parameters.
    *
          INFO = 0
          IF( N.LT.0 ) THEN
             INFO = -1
          ELSE IF( NRHS.LT.0 ) THEN
             INFO = -2
          ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
             INFO = -6
          END IF
          IF( INFO.NE.0 ) THEN
             CALL XERBLA( 'ZPTSV ', -INFO )
             RETURN
          END IF
    *
    *     Compute the L*D*L' (or U'*D*U) factorization of A.
    *
          CALL ZPTTRF( N, D, E, INFO )
          IF( INFO.EQ.0 ) THEN
    *
    *        Solve the system A*X = B, overwriting B with X.
    *
             CALL ZPTTRS( 'Lower', N, NRHS, D, E, B, LDB, INFO )
          END IF
          RETURN
    *
    *     End of ZPTSV
    *
          END