DSPCON(3F)DSPCON(3F)NAME
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 structure 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 matrix A, computed
as RCOND = 1/(ANORM * AINVNM), where AINVNM is an estimate of the
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DSPCON(3F)DSPCON(3F)
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 illegal value
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