DSPCON - estimate the reciprocal of the condition number
(in the 1-norm) of a real symmetric packed matrix A using
the factorization A = U*D*U**T or A = L*D*L**T computed by
DSPTRF
SYNOPSIS
SUBROUTINE DSPCON( UPLO, N, AP, IPIV, ANORM, RCOND, WORK,
IWORK, INFO )
CHARACTER UPLO
INTEGER INFO, N
DOUBLE PRECISION ANORM, RCOND
INTEGER IPIV( * ), IWORK( * )
DOUBLE PRECISION AP( * ), WORK( * )
PURPOSE
DSPCON estimates the reciprocal of the condition number
(in the 1-norm) of a real symmetric packed matrix A using
the factorization A = U*D*U**T or A = L*D*L**T computed by
DSPTRF. 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
UPLO (input) CHARACTER*1
Specifies whether the details of the factorization
are stored as an upper or lower triangular matrix.
= 'U': Upper triangular, form is A = U*D*U**T;
= 'L': Lower triangular, form is A = L*D*L**T.
N (input) INTEGER
The order of the matrix A. N >= 0.
AP (input) DOUBLE PRECISION array, dimension
(N*(N+1)/2)
The block diagonal matrix D and the multipliers
used to obtain the factor U or L as computed by
DSPTRF, stored as a packed triangular matrix.
IPIV (input) INTEGER array, dimension (N)
Details of the interchanges and the block struc
ture of D as determined by DSPTRF.
ANORM (input) DOUBLE PRECISION
The 1-norm of the original matrix A.
RCOND (output) DOUBLE PRECISION
The reciprocal of the condition number of the
where AINVNM is an estimate of the 1-norm 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 i-th argument had an ille
gal value
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