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## zgttrf()

subroutine zgttrf | ( | integer | n,
|  | complex*16, dimension( * ) | dl,
|  | complex*16, dimension( * ) | d,
|  | complex*16, dimension( * ) | du,
|  | complex*16, dimension( * ) | du2,
|  | integer, dimension( * ) | ipiv,
|  | integer | info )

ZGTTRF

Download ZGTTRF + dependencies [TGZ] [ZIP] [TXT]

Purpose:

      !>
      !> ZGTTRF computes an LU factorization of a complex tridiagonal matrix A
      !> using elimination with partial pivoting and row interchanges.
      !>
      !> The factorization has the form
      !>    A = L * U
      !> where L is a product of permutation and unit lower bidiagonal
      !> matrices and U is upper triangular with nonzeros in only the main
      !> diagonal and first two superdiagonals.
      !>

Parameters

  [in]

  N

      !>          N is INTEGER
      !>          The order of the matrix A.
      !>

  [in,out]

  DL

      !>          DL is COMPLEX*16 array, dimension (N-1)
      !>          On entry, DL must contain the (n-1) sub-diagonal elements of
      !>          A.
      !>
      !>          On exit, DL is overwritten by the (n-1) multipliers that
      !>          define the matrix L from the LU factorization of A.
      !>

  [in,out]

  D

      !>          D is COMPLEX*16 array, dimension (N)
      !>          On entry, D must contain the diagonal elements of A.
      !>
      !>          On exit, D is overwritten by the n diagonal elements of the
      !>          upper triangular matrix U from the LU factorization of A.
      !>

  [in,out]

  DU

      !>          DU is COMPLEX*16 array, dimension (N-1)
      !>          On entry, DU must contain the (n-1) super-diagonal elements
      !>          of A.
      !>
      !>          On exit, DU is overwritten by the (n-1) elements of the first
      !>          super-diagonal of U.
      !>

  [out]

  DU2

      !>          DU2 is COMPLEX*16 array, dimension (N-2)
      !>          On exit, DU2 is overwritten by the (n-2) elements of the
      !>          second super-diagonal of U.
      !>

  [out]

  IPIV

      !>          IPIV is INTEGER array, dimension (N)
      !>          The pivot indices; for 1 <= i <= n, row i of the matrix was
      !>          interchanged with row IPIV(i).  IPIV(i) will always be either
      !>          i or i+1; IPIV(i) = i indicates a row interchange was not
      !>          required.
      !>

  [out]

  INFO

      !>          INFO is INTEGER
      !>          = 0:  successful exit
      !>          < 0:  if INFO = -k, the k-th argument had an illegal value
      !>          > 0:  if INFO = k, U(k,k) is exactly zero. The factorization
      !>                has been completed, but the factor U is exactly
      !>                singular, and division by zero will occur if it is used
      !>                to solve a system of equations.
      !>

Author
  Univ. of Tennessee
  Univ. of California Berkeley
  Univ. of Colorado Denver
  NAG Ltd.