sgtcon (l)  Linux Manuals
sgtcon: estimates the reciprocal of the condition number of a real tridiagonal matrix A using the LU factorization as computed by SGTTRF
Command to display sgtcon
manual in Linux: $ man l sgtcon
NAME
SGTCON  estimates the reciprocal of the condition number of a real tridiagonal matrix A using the LU factorization as computed by SGTTRF
SYNOPSIS
 SUBROUTINE SGTCON(

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

CHARACTER
NORM

INTEGER
INFO, N

REAL
ANORM, RCOND

INTEGER
IPIV( * ), IWORK( * )

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

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

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

The (n1) elements of the first superdiagonal of U.
 DU2 (input) REAL 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) REAL 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 sgtcon
 sgtcon (3)
 sgtrfs (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
 sgtsv (l)  solves the equation A*X = B,
 sgtsvx (l)  uses the LU factorization to compute the solution to a real system of linear equations A * X = B or A**T * X = B,
 sgttrf (l)  computes an LU factorization of a real tridiagonal matrix A using elimination with partial pivoting and row interchanges
 sgttrs (l)  solves one of the systems of equations A*X = B or Aaq*X = B,
 sgtts2 (l)  solves one of the systems of equations A*X = B or Aaq*X = B,
 sgbbrd (l)  reduces a real general mbyn band matrix A to upper bidiagonal form B by an orthogonal transformation