.TH DGECON 1 "November 2006" " LAPACK routine (version 3.1) " " LAPACK routine (version 3.1) " .SH NAME DGECON - the reciprocal of the condition number of a general real matrix A, in either the 1-norm or the infinity-norm, using the LU factorization computed by DGETRF .SH SYNOPSIS .TP 19 SUBROUTINE DGECON( NORM, N, A, LDA, ANORM, RCOND, WORK, IWORK, INFO ) .TP 19 .ti +4 CHARACTER NORM .TP 19 .ti +4 INTEGER INFO, LDA, N .TP 19 .ti +4 DOUBLE PRECISION ANORM, RCOND .TP 19 .ti +4 INTEGER IWORK( * ) .TP 19 .ti +4 DOUBLE PRECISION A( LDA, * ), WORK( * ) .SH PURPOSE DGECON estimates the reciprocal of the condition number of a general real matrix A, in either the 1-norm or the infinity-norm, using the LU factorization computed by DGETRF. An estimate is obtained for norm(inv(A)), and the reciprocal of the condition number is computed as .br RCOND = 1 / ( norm(A) * norm(inv(A)) ). .br .SH ARGUMENTS .TP 8 NORM (input) CHARACTER*1 Specifies whether the 1-norm condition number or the infinity-norm condition number is required: .br = \(aq1\(aq or \(aqO\(aq: 1-norm; .br = \(aqI\(aq: Infinity-norm. .TP 8 N (input) INTEGER The order of the matrix A. N >= 0. .TP 8 A (input) DOUBLE PRECISION array, dimension (LDA,N) The factors L and U from the factorization A = P*L*U as computed by DGETRF. .TP 8 LDA (input) INTEGER The leading dimension of the array A. LDA >= max(1,N). .TP 8 ANORM (input) DOUBLE PRECISION If NORM = \(aq1\(aq or \(aqO\(aq, the 1-norm of the original matrix A. If NORM = \(aqI\(aq, the infinity-norm of the original matrix A. .TP 8 RCOND (output) DOUBLE PRECISION The reciprocal of the condition number of the matrix A, computed as RCOND = 1/(norm(A) * norm(inv(A))). .TP 8 WORK (workspace) DOUBLE PRECISION array, dimension (4*N) .TP 8 IWORK (workspace) INTEGER array, dimension (N) .TP 8 INFO (output) INTEGER = 0: successful exit .br < 0: if INFO = -i, the i-th argument had an illegal value