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

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

CHARACTER
NORM

INTEGER
INFO, N

DOUBLE
PRECISION ANORM, RCOND

INTEGER
IPIV( * ), IWORK( * )

DOUBLE
PRECISION D( * ), DL( * ), DU( * ), DU2( * ), WORK( * )
PURPOSE
DGTCON estimates the reciprocal of the condition number of a real
tridiagonal matrix A using the LU factorization as computed by
DGTTRF.
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) DOUBLE PRECISION array, dimension (N1)

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

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

The (n1) elements of the first superdiagonal of U.
 DU2 (input) DOUBLE PRECISION 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) DOUBLE PRECISION

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

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) DOUBLE PRECISION array, dimension (2*N)

 IWORK (workspace) INTEGER array, dimension (N)

 INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = i, the ith argument had an illegal value
Pages related to dgtcon
 dgtcon (3)
 dgtrfs (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
 dgtsv (l)  solves the equation A*X = B,
 dgtsvx (l)  uses the LU factorization to compute the solution to a real system of linear equations A * X = B or A**T * X = B,
 dgttrf (l)  computes an LU factorization of a real tridiagonal matrix A using elimination with partial pivoting and row interchanges
 dgttrs (l)  solves one of the systems of equations A*X = B or Aaq*X = B,
 dgtts2 (l)  solves one of the systems of equations A*X = B or Aaq*X = B,
 dgbbrd (l)  reduces a real general mbyn band matrix A to upper bidiagonal form B by an orthogonal transformation