ctrcon (l) - Linux Man Pages

ctrcon: estimates the reciprocal of the condition number of a triangular matrix A, in either the 1-norm or the infinity-norm

NAME

CTRCON - estimates the reciprocal of the condition number of a triangular matrix A, in either the 1-norm or the infinity-norm

SYNOPSIS

SUBROUTINE CTRCON(
NORM, UPLO, DIAG, N, A, LDA, RCOND, WORK, RWORK, INFO )

    
CHARACTER DIAG, NORM, UPLO

    
INTEGER INFO, LDA, N

    
REAL RCOND

    
REAL RWORK( * )

    
COMPLEX A( LDA, * ), WORK( * )

PURPOSE

CTRCON estimates the reciprocal of the condition number of a triangular matrix A, in either the 1-norm or the infinity-norm. The norm of A is computed and an estimate is obtained for norm(inv(A)), then the reciprocal of the condition number is computed as

RCOND norm(A) norm(inv(A)) ).

ARGUMENTS

NORM (input) CHARACTER*1
Specifies whether the 1-norm condition number or the infinity-norm condition number is required:
= aq1aq or aqOaq: 1-norm;
= aqIaq: Infinity-norm.
UPLO (input) CHARACTER*1

= aqUaq: A is upper triangular;
= aqLaq: A is lower triangular.
DIAG (input) CHARACTER*1

= aqNaq: A is non-unit triangular;
= aqUaq: A is unit triangular.
N (input) INTEGER
The order of the matrix A. N >= 0.
A (input) COMPLEX array, dimension (LDA,N)
The triangular matrix A. If UPLO = aqUaq, the leading N-by-N upper triangular part of the array A contains the upper triangular matrix, and the strictly lower triangular part of A is not referenced. If UPLO = aqLaq, the leading N-by-N lower triangular part of the array A contains the lower triangular matrix, and the strictly upper triangular part of A is not referenced. If DIAG = aqUaq, the diagonal elements of A are also not referenced and are assumed to be 1.
LDA (input) INTEGER
The leading dimension of the array A. LDA >= max(1,N).
RCOND (output) REAL
The reciprocal of the condition number of the matrix A, computed as RCOND = 1/(norm(A) * norm(inv(A))).
WORK (workspace) COMPLEX array, dimension (2*N)
RWORK (workspace) REAL array, dimension (N)
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value