STBCON - estimate the reciprocal of the condition number
of a triangular band matrix A, in either the 1-norm or the
infinity-norm
SYNOPSIS
SUBROUTINE STBCON( NORM, UPLO, DIAG, N, KD, AB, LDAB,
RCOND, WORK, IWORK, INFO )
CHARACTER DIAG, NORM, UPLO
INTEGER INFO, KD, LDAB, N
REAL RCOND
INTEGER IWORK( * )
REAL AB( LDAB, * ), WORK( * )
PURPOSE
STBCON estimates the reciprocal of the condition number of
a triangular band matrix A, in either the 1-norm or the
infinity-norm. The norm of A is computed and an estimate
is obtained for norm(inv(A)), then the reciprocal of the
condition number is computed as
RCOND = 1 / ( norm(A) * norm(inv(A)) ).
ARGUMENTS
NORM (input) 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.
UPLO (input) CHARACTER*1
= 'U': A is upper triangular;
= 'L': A is lower triangular.
DIAG (input) CHARACTER*1
= 'N': A is non-unit triangular;
= 'U': A is unit triangular.
N (input) INTEGER
The order of the matrix A. N >= 0.
KD (input) INTEGER
The number of superdiagonals or subdiagonals of
the triangular band matrix A. KD >= 0.
AB (input) REAL array, dimension (LDAB,N)
The upper or lower triangular band matrix A,
stored in the first kd+1 rows of the array. The j-
th column of A is stored in the j-th column of the
= A(i,j) for max(1,j-kd)<=i<=j; if UPLO = 'L',
AB(1+i-j,j) = A(i,j) for j<=i<=min(n,j+kd). If
DIAG = 'U', the diagonal elements of A are not
referenced and are assumed to be 1.
LDAB (input) INTEGER
The leading dimension of the array AB. LDAB >=
KD+1.
RCOND (output) REAL
The reciprocal of the condition number of the
matrix A, computed as RCOND = 1/(norm(A) *
norm(inv(A))).
WORK (workspace) REAL array, dimension (3*N)
IWORK (workspace) INTEGER array, dimension (N)
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an ille
gal value
Man(1) output converted with
man2html