dgbcon (l)  Linux Manuals
dgbcon: estimates the reciprocal of the condition number of a real general band matrix A, in either the 1norm or the infinitynorm,
NAME
DGBCON  estimates the reciprocal of the condition number of a real general band matrix A, in either the 1norm or the infinitynorm,SYNOPSIS
 SUBROUTINE DGBCON(
 NORM, N, KL, KU, AB, LDAB, IPIV, ANORM, RCOND, WORK, IWORK, INFO )
 CHARACTER NORM
 INTEGER INFO, KL, KU, LDAB, N
 DOUBLE PRECISION ANORM, RCOND
 INTEGER IPIV( * ), IWORK( * )
 DOUBLE PRECISION AB( LDAB, * ), WORK( * )
PURPOSE
DGBCON estimates the reciprocal of the condition number of a real general band matrix A, in either the 1norm or the infinitynorm, using the LU factorization computed by DGBTRF.An estimate is obtained for norm(inv(A)), and the reciprocal of the condition number is computed as
RCOND
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.
 KL (input) INTEGER
 The number of subdiagonals within the band of A. KL >= 0.
 KU (input) INTEGER
 The number of superdiagonals within the band of A. KU >= 0.
 AB (input) DOUBLE PRECISION array, dimension (LDAB,N)
 Details of the LU factorization of the band matrix A, as computed by DGBTRF. U is stored as an upper triangular band matrix with KL+KU superdiagonals in rows 1 to KL+KU+1, and the multipliers used during the factorization are stored in rows KL+KU+2 to 2*KL+KU+1.
 LDAB (input) INTEGER
 The leading dimension of the array AB. LDAB >= 2*KL+KU+1.
 IPIV (input) INTEGER array, dimension (N)
 The pivot indices; for 1 <= i <= N, row i of the matrix was interchanged with row IPIV(i).
 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/(norm(A) * norm(inv(A))).
 WORK (workspace) DOUBLE PRECISION array, dimension (3*N)
 IWORK (workspace) INTEGER array, dimension (N)
 INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = i, the ith argument had an illegal value