checon_3()

subroutine checon_3	(	character	uplo,
		integer	n,
		complex, dimension( lda, * )	a,
		integer	lda,
		complex, dimension( * )	e,
		integer, dimension( * )	ipiv,
		real	anorm,
		real	rcond,
		complex, dimension( * )	work,
		integer	info )

CHECON_3

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Purpose:

!> CHECON_3 estimates the reciprocal of the condition number (in the
!> 1-norm) of a complex Hermitian matrix A using the factorization
!> computed by CHETRF_RK or CHETRF_BK:
!>
!>    A = P*U*D*(U**H)*(P**T) or A = P*L*D*(L**H)*(P**T),
!>
!> where U (or L) is unit upper (or lower) triangular matrix,
!> U**H (or L**H) is the conjugate of U (or L), P is a permutation
!> matrix, P**T is the transpose of P, and D is Hermitian and block
!> diagonal with 1-by-1 and 2-by-2 diagonal blocks.
!>
!> An estimate is obtained for norm(inv(A)), and the reciprocal of the
!> condition number is computed as RCOND = 1 / (ANORM * norm(inv(A))).
!> This routine uses BLAS3 solver CHETRS_3.
!> 

Parameters

[in]	UPLO	!> UPLO is CHARACTER*1 !> Specifies whether the details of the factorization are !> stored as an upper or lower triangular matrix: !> = 'U': Upper triangular, form is A = P*U*D*(U**H)*(P**T); !> = 'L': Lower triangular, form is A = P*L*D*(L**H)*(P**T). !>
[in]	N	!> N is INTEGER !> The order of the matrix A. N >= 0. !>
[in]	A	!> A is COMPLEX array, dimension (LDA,N) !> Diagonal of the block diagonal matrix D and factors U or L !> as computed by CHETRF_RK and CHETRF_BK: !> a) ONLY diagonal elements of the Hermitian block diagonal !> matrix D on the diagonal of A, i.e. D(k,k) = A(k,k); !> (superdiagonal (or subdiagonal) elements of D !> should be provided on entry in array E), and !> b) If UPLO = 'U': factor U in the superdiagonal part of A. !> If UPLO = 'L': factor L in the subdiagonal part of A. !>
[in]	LDA	!> LDA is INTEGER !> The leading dimension of the array A. LDA >= max(1,N). !>
[in]	E	!> E is COMPLEX array, dimension (N) !> On entry, contains the superdiagonal (or subdiagonal) !> elements of the Hermitian block diagonal matrix D !> with 1-by-1 or 2-by-2 diagonal blocks, where !> If UPLO = 'U': E(i) = D(i-1,i),i=2:N, E(1) not referenced; !> If UPLO = 'L': E(i) = D(i+1,i),i=1:N-1, E(N) not referenced. !> !> NOTE: For 1-by-1 diagonal block D(k), where !> 1 <= k <= N, the element E(k) is not referenced in both !> UPLO = 'U' or UPLO = 'L' cases. !>
[in]	IPIV	!> IPIV is INTEGER array, dimension (N) !> Details of the interchanges and the block structure of D !> as determined by CHETRF_RK or CHETRF_BK. !>
[in]	ANORM	!> ANORM is REAL !> The 1-norm of the original matrix A. !>
[out]	RCOND	!> RCOND is 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. !>
[out]	WORK	!> WORK is COMPLEX array, dimension (2*N) !>
[out]	INFO	!> INFO is INTEGER !> = 0: successful exit !> < 0: if INFO = -i, the i-th argument had an illegal value !>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Contributors:

!>
!>  June 2017,  Igor Kozachenko,
!>                  Computer Science Division,
!>                  University of California, Berkeley
!>
!>  September 2007, Sven Hammarling, Nicholas J. Higham, Craig Lucas,
!>                  School of Mathematics,
!>                  University of Manchester
!>
!>