LAPACK 3.12.0
LAPACK: Linear Algebra PACKage
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◆ cgecon()

subroutine cgecon ( character norm,
integer n,
complex, dimension( lda, * ) a,
integer lda,
real anorm,
real rcond,
complex, dimension( * ) work,
real, dimension( * ) rwork,
integer info )

CGECON

Download CGECON + dependencies [TGZ] [ZIP] [TXT]

Purpose:
!>
!> CGECON estimates the reciprocal of the condition number of a general
!> complex matrix A, in either the 1-norm or the infinity-norm, using
!> the LU factorization computed by CGETRF.
!>
!> An estimate is obtained for norm(inv(A)), and the reciprocal of the
!> condition number is computed as
!>    RCOND = 1 / ( norm(A) * norm(inv(A)) ).
!>
Parameters
[in]NORM
!>          NORM is 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.
!>
[in]N
!>          N is INTEGER
!>          The order of the matrix A.  N >= 0.
!>
[in]A
!>          A is COMPLEX array, dimension (LDA,N)
!>          The factors L and U from the factorization A = P*L*U
!>          as computed by CGETRF.
!>
[in]LDA
!>          LDA is INTEGER
!>          The leading dimension of the array A.  LDA >= max(1,N).
!>
[in]ANORM
!>          ANORM is REAL
!>          If NORM = '1' or 'O', the 1-norm of the original matrix A.
!>          If NORM = 'I', the infinity-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/(norm(A) * norm(inv(A))).
!>
[out]WORK
!>          WORK is COMPLEX array, dimension (2*N)
!>
[out]RWORK
!>          RWORK is REAL array, dimension (2*N)
!>
[out]INFO
!>          INFO is INTEGER
!>          = 0:  successful exit
!>          < 0:  if INFO = -i, the i-th argument had an illegal value.
!>                NaNs are illegal values for ANORM, and they propagate to
!>                the output parameter RCOND.
!>                Infinity is illegal for ANORM, and it propagates to the output
!>                parameter RCOND as 0.
!>          = 1:  if RCOND = NaN, or
!>                   RCOND = Inf, or
!>                   the computed norm of the inverse of A is 0.
!>                In the latter, RCOND = 0 is returned.
!>
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.