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sgtcon.f(3) LAPACK sgtcon.f(3)

NAME

sgtcon.f -

SYNOPSIS

Functions/Subroutines


subroutine sgtcon (NORM, N, DL, D, DU, DU2, IPIV, ANORM, RCOND, WORK, IWORK, INFO)
SGTCON

Function/Subroutine Documentation

subroutine sgtcon (characterNORM, integerN, real, dimension( * )DL, real, dimension( * )D, real, dimension( * )DU, real, dimension( * )DU2, integer, dimension( * )IPIV, realANORM, realRCOND, real, dimension( * )WORK, integer, dimension( * )IWORK, integerINFO)

SGTCON

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))).

Parameters:

NORM


NORM is CHARACTER*1
Specifies whether the 1-norm condition number or the
infinity-norm condition number is required:
= '1' or 'O': 1-norm;
= 'I': Infinity-norm.

N


N is INTEGER
The order of the matrix A. N >= 0.

DL


DL is REAL array, dimension (N-1)
The (n-1) multipliers that define the matrix L from the
LU factorization of A as computed by SGTTRF.

D


D is REAL array, dimension (N)
The n diagonal elements of the upper triangular matrix U from
the LU factorization of A.

DU


DU is REAL array, dimension (N-1)
The (n-1) elements of the first superdiagonal of U.

DU2


DU2 is REAL array, dimension (N-2)
The (n-2) elements of the second superdiagonal 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.

ANORM


ANORM is REAL
If NORM = '1' or 'O', the 1-norm of the original matrix A.
If NORM = 'I', the infinity-norm of the original matrix A.

RCOND


RCOND is REAL
The reciprocal of the condition number of the matrix A,
computed as RCOND = 1/(ANORM * AINVNM), where AINVNM is an
estimate of the 1-norm of inv(A) computed in this routine.

WORK


WORK is REAL array, dimension (2*N)

IWORK


IWORK is INTEGER array, dimension (N)

INFO


INFO is INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

September 2012

Definition at line 146 of file sgtcon.f.

Author

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Tue Sep 25 2012 Version 3.4.2