DGTCON - Online Linux Manual Page

Section : 1
Updated : November 2008
Source : LAPACK routine (version 3.2)
Note : LAPACK routine (version 3.2)
NAMEDGTCON - estimates the reciprocal of the condition number of a real tridiagonal matrix A using the LU factorization as computed by DGTTRF
SYNOPSISSUBROUTINE DGTCON(  NORM, N, DL, D, DU, DU2, IPIV, ANORM, RCOND, WORK, IWORK, INFO )  CHARACTER NORM  INTEGER INFO, N  DOUBLE PRECISION ANORM, RCOND  INTEGER IPIV( * ), IWORK( * )  DOUBLE PRECISION D( * ), DL( * ), DU( * ), DU2( * ), WORK( * )
PURPOSEDGTCON estimates the reciprocal of the condition number of a real tridiagonal matrix A using the LU factorization as computed by DGTTRF. An estimate is obtained for norm(inv(A)), and the reciprocal of the condition number is computed as RCOND = 1 / (ANORM * norm(inv(A))).
ARGUMENTSNORM (input) 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. N (input) INTEGER  The order of the matrix A. N >= 0. DL (input) DOUBLE PRECISION array, dimension (N-1)  The (n-1) multipliers that define the matrix L from the LU factorization of A as computed by DGTTRF. D (input) DOUBLE PRECISION array, dimension (N)  The n diagonal elements of the upper triangular matrix U from the LU factorization of A. DU (input) DOUBLE PRECISION array, dimension (N-1)  The (n-1) elements of the first superdiagonal of U. DU2 (input) DOUBLE PRECISION array, dimension (N-2)  The (n-2) elements of the second superdiagonal of U. IPIV (input) INTEGER array, dimension (N)  The pivot indices; for 1 <= i <= n, row i of the matrix was interchanged with row IPIV(i). IPIV(i) will always be either i or i+1; IPIV(i) = i indicates a row interchange was not required. ANORM (input) DOUBLE PRECISION  If NORM = '1' or 'O', the 1-norm of the original matrix A. If NORM = 'I', the infinity-norm of the original matrix A. RCOND (output) DOUBLE PRECISION  The reciprocal of the condition number of the matrix A, computed as RCOND = 1/(ANORM * AINVNM), where AINVNM is an estimate of the 1-norm of inv(A) computed in this routine. WORK (workspace) DOUBLE PRECISION array, dimension (2*N)  IWORK (workspace) INTEGER array, dimension (N)  INFO (output) INTEGER  = 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value 0
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