NAME

       dgttrf.f -

SYNOPSIS

   Functions/Subroutines
       subroutine dgttrf (N, DL, D, DU, DU2, IPIV, INFO)
           DGTTRF

Function/Subroutine Documentation

   subroutine dgttrf (integerN, double precision, dimension( * )DL, double precision, dimension(
       * )D, double precision, dimension( * )DU, double precision, dimension( * )DU2, integer,
       dimension( * )IPIV, integerINFO)
       DGTTRF

       Purpose:

            DGTTRF computes an LU factorization of a real 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:
           N

                     N is INTEGER
                     The order of the matrix A.

           DL

                     DL is DOUBLE PRECISION 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.

           D

                     D is DOUBLE PRECISION 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.

           DU

                     DU is DOUBLE PRECISION 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.

           DU2

                     DU2 is DOUBLE PRECISION array, dimension (N-2)
                     On exit, DU2 is overwritten by the (n-2) elements of the
                     second super-diagonal of U.

           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.

           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.

       Date:
           September 2012

       Definition at line 125 of file dgttrf.f.

Author

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