cgttrf man page on IRIX

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CGTTRF(3F)							    CGTTRF(3F)

NAME
     CGTTRF - compute an LU factorization of a complex tridiagonal matrix A
     using elimination with partial pivoting and row interchanges

SYNOPSIS
     SUBROUTINE CGTTRF( N, DL, D, DU, DU2, IPIV, INFO )

	 INTEGER	INFO, N

	 INTEGER	IPIV( * )

	 COMPLEX	D( * ), DL( * ), DU( * ), DU2( * )

PURPOSE
     CGTTRF 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.

ARGUMENTS
     N	     (input) INTEGER
	     The order of the matrix A.	 N >= 0.

     DL	     (input/output) COMPLEX array, dimension (N-1)
	     On entry, DL must contain the (n-1) subdiagonal 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	     (input/output) COMPLEX 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	     (input/output) COMPLEX array, dimension (N-1)
	     On entry, DU must contain the (n-1) superdiagonal elements of A.
	     On exit, DU is overwritten by the (n-1) elements of the first
	     superdiagonal of U.

     DU2     (output) COMPLEX array, dimension (N-2)
	     On exit, DU2 is overwritten by the (n-2) elements of the second
	     superdiagonal of U.

     IPIV    (output) 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.

									Page 1

CGTTRF(3F)							    CGTTRF(3F)

     INFO    (output) INTEGER
	     = 0:  successful exit
	     < 0:  if INFO = -i, the i-th argument had an illegal value
	     > 0:  if INFO = i, U(i,i) 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.

									Page 2

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