cgtcon (l)  Linux Man Pages
cgtcon: estimates the reciprocal of the condition number of a complex tridiagonal matrix A using the LU factorization as computed by CGTTRF
Command to display cgtcon
manual in Linux: $ man l cgtcon
NAME
CGTCON  estimates the reciprocal of the condition number of a complex tridiagonal matrix A using the LU factorization as computed by CGTTRF
SYNOPSIS
 SUBROUTINE CGTCON(

NORM, N, DL, D, DU, DU2, IPIV, ANORM, RCOND,
WORK, INFO )

CHARACTER
NORM

INTEGER
INFO, N

REAL
ANORM, RCOND

INTEGER
IPIV( * )

COMPLEX
D( * ), DL( * ), DU( * ), DU2( * ), WORK( * )
PURPOSE
CGTCON estimates the reciprocal of the condition number of a complex
tridiagonal matrix A using the LU factorization as computed by
CGTTRF.
An estimate is obtained for norm(inv(A)), and the reciprocal of the
condition number is computed as RCOND = 1 / (ANORM * norm(inv(A))).
ARGUMENTS
 NORM (input) CHARACTER*1

Specifies whether the 1norm condition number or the
infinitynorm condition number is required:
= aq1aq or aqOaq: 1norm;
= aqIaq: Infinitynorm.
 N (input) INTEGER

The order of the matrix A. N >= 0.
 DL (input) COMPLEX array, dimension (N1)

The (n1) multipliers that define the matrix L from the
LU factorization of A as computed by CGTTRF.
 D (input) COMPLEX array, dimension (N)

The n diagonal elements of the upper triangular matrix U from
the LU factorization of A.
 DU (input) COMPLEX array, dimension (N1)

The (n1) elements of the first superdiagonal of U.
 DU2 (input) COMPLEX array, dimension (N2)

The (n2) elements of the second superdiagonal of U.
 IPIV (input) 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.
 ANORM (input) REAL

If NORM = aq1aq or aqOaq, the 1norm of the original matrix A.
If NORM = aqIaq, the infinitynorm of the original matrix A.
 RCOND (output) REAL

The reciprocal of the condition number of the matrix A,
computed as RCOND = 1/(ANORM * AINVNM), where AINVNM is an
estimate of the 1norm of inv(A) computed in this routine.
 WORK (workspace) COMPLEX array, dimension (2*N)

 INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = i, the ith argument had an illegal value
Pages related to cgtcon
 cgtcon (3)
 cgtrfs (l)  improves the computed solution to a system of linear equations when the coefficient matrix is tridiagonal, and provides error bounds and backward error estimates for the solution
 cgtsv (l)  solves the equation A*X = B,
 cgtsvx (l)  uses the LU factorization to compute the solution to a complex system of linear equations A * X = B, A**T * X = B, or A**H * X = B,
 cgttrf (l)  computes an LU factorization of a complex tridiagonal matrix A using elimination with partial pivoting and row interchanges
 cgttrs (l)  solves one of the systems of equations A * X = B, A**T * X = B, or A**H * X = B,
 cgtts2 (l)  solves one of the systems of equations A * X = B, A**T * X = B, or A**H * X = B,
 cgbbrd (l)  reduces a complex general mbyn band matrix A to real upper bidiagonal form B by a unitary transformation