SSYCON(3F)SSYCON(3F)NAME
SSYCON - estimate the reciprocal of the condition number (in the 1-norm)
of a real symmetric matrix A using the factorization A = U*D*U**T or A =
L*D*L**T computed by SSYTRF
SYNOPSIS
SUBROUTINE SSYCON( UPLO, N, A, LDA, IPIV, ANORM, RCOND, WORK, IWORK, INFO
)
CHARACTER UPLO
INTEGER INFO, LDA, N
REAL ANORM, RCOND
INTEGER IPIV( * ), IWORK( * )
REAL A( LDA, * ), WORK( * )
PURPOSE
SSYCON estimates the reciprocal of the condition number (in the 1-norm)
of a real symmetric matrix A using the factorization A = U*D*U**T or A =
L*D*L**T computed by SSYTRF.
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.
A (input) REAL array, dimension (LDA,N)
The block diagonal matrix D and the multipliers used to obtain
the factor U or L as computed by SSYTRF.
LDA (input) INTEGER
The leading dimension of the array A. LDA >= max(1,N).
IPIV (input) INTEGER array, dimension (N)
Details of the interchanges and the block structure of D as
determined by SSYTRF.
ANORM (input) REAL
The 1-norm of the original matrix A.
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SSYCON(3F)SSYCON(3F)
RCOND (output) 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 (workspace) REAL 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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