1DTRCON(1)                LAPACK routine (version 3.1)                DTRCON(1)
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NAME

6       DTRCON  - the reciprocal of the condition number of a triangular matrix
7       A, in either the 1-norm or the infinity-norm
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SYNOPSIS

10       SUBROUTINE DTRCON( NORM, UPLO, DIAG, N, A,  LDA,  RCOND,  WORK,  IWORK,
11                          INFO )
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13           CHARACTER      DIAG, NORM, UPLO
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15           INTEGER        INFO, LDA, N
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17           DOUBLE         PRECISION RCOND
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19           INTEGER        IWORK( * )
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21           DOUBLE         PRECISION A( LDA, * ), WORK( * )
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PURPOSE

24       DTRCON estimates the reciprocal of the condition number of a triangular
25       matrix A, in either the 1-norm or the infinity-norm.
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27       The norm of A is computed and an estimate is obtained for norm(inv(A)),
28       then the reciprocal of the condition number is computed as
29          RCOND = 1 / ( norm(A) * norm(inv(A)) ).
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ARGUMENTS

33       NORM    (input) CHARACTER*1
34               Specifies  whether the 1-norm condition number or the infinity-
35               norm condition number is required:
36               = '1' or 'O':  1-norm;
37               = 'I':         Infinity-norm.
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39       UPLO    (input) CHARACTER*1
40               = 'U':  A is upper triangular;
41               = 'L':  A is lower triangular.
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43       DIAG    (input) CHARACTER*1
44               = 'N':  A is non-unit triangular;
45               = 'U':  A is unit triangular.
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47       N       (input) INTEGER
48               The order of the matrix A.  N >= 0.
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50       A       (input) DOUBLE PRECISION array, dimension (LDA,N)
51               The triangular matrix A.  If UPLO =  'U',  the  leading  N-by-N
52               upper  triangular part of the array A contains the upper trian‐
53               gular matrix, and the strictly lower triangular part  of  A  is
54               not referenced.  If UPLO = 'L', the leading N-by-N lower trian‐
55               gular part of the array A contains the lower triangular matrix,
56               and  the strictly upper triangular part of A is not referenced.
57               If DIAG = 'U', the diagonal elements of A are also  not  refer‐
58               enced and are assumed to be 1.
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60       LDA     (input) INTEGER
61               The leading dimension of the array A.  LDA >= max(1,N).
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63       RCOND   (output) DOUBLE PRECISION
64               The  reciprocal  of  the condition number of the matrix A, com‐
65               puted as RCOND = 1/(norm(A) * norm(inv(A))).
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67       WORK    (workspace) DOUBLE PRECISION array, dimension (3*N)
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69       IWORK   (workspace) INTEGER array, dimension (N)
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71       INFO    (output) INTEGER
72               = 0:  successful exit
73               < 0:  if INFO = -i, the i-th argument had an illegal value
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77 LAPACK routine (version 3.1)    November 2006                       DTRCON(1)
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