dtrcon (l)  Linux Man Pages
dtrcon: estimates the reciprocal of the condition number of a triangular matrix A, in either the 1norm or the infinitynorm
NAME
DTRCON  estimates the reciprocal of the condition number of a triangular matrix A, in either the 1norm or the infinitynormSYNOPSIS
 SUBROUTINE DTRCON(
 NORM, UPLO, DIAG, N, A, LDA, RCOND, WORK, IWORK, INFO )
 CHARACTER DIAG, NORM, UPLO
 INTEGER INFO, LDA, N
 DOUBLE PRECISION RCOND
 INTEGER IWORK( * )
 DOUBLE PRECISION A( LDA, * ), WORK( * )
PURPOSE
DTRCON estimates the reciprocal of the condition number of a triangular matrix A, in either the 1norm or the infinitynorm. The norm of A is computed and an estimate is obtained for norm(inv(A)), then the reciprocal of the condition number is computed asRCOND
ARGUMENTS
 NORM (input) CHARACTER*1

Specifies whether the 1norm condition number or the
infinitynorm condition number is required:
= aq1aq or aqOaq: 1norm;
= aqIaq: Infinitynorm.  UPLO (input) CHARACTER*1

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

= aqNaq: A is nonunit triangular;
= aqUaq: A is unit triangular.  N (input) INTEGER
 The order of the matrix A. N >= 0.
 A (input) DOUBLE PRECISION array, dimension (LDA,N)
 The triangular matrix A. If UPLO = aqUaq, the leading NbyN 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 NbyN 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) DOUBLE PRECISION
 The reciprocal of the condition number of the matrix A, computed as RCOND = 1/(norm(A) * norm(inv(A))).
 WORK (workspace) DOUBLE PRECISION array, dimension (3*N)
 IWORK (workspace) INTEGER array, dimension (N)
 INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = i, the ith argument had an illegal value