ctbcon (l)  Linux Manuals
ctbcon: estimates the reciprocal of the condition number of a triangular band matrix A, in either the 1norm or the infinitynorm
NAME
CTBCON  estimates the reciprocal of the condition number of a triangular band matrix A, in either the 1norm or the infinitynormSYNOPSIS
 SUBROUTINE CTBCON(
 NORM, UPLO, DIAG, N, KD, AB, LDAB, RCOND, WORK, RWORK, INFO )
 CHARACTER DIAG, NORM, UPLO
 INTEGER INFO, KD, LDAB, N
 REAL RCOND
 REAL RWORK( * )
 COMPLEX AB( LDAB, * ), WORK( * )
PURPOSE
CTBCON estimates the reciprocal of the condition number of a triangular band 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.
 KD (input) INTEGER
 The number of superdiagonals or subdiagonals of the triangular band matrix A. KD >= 0.
 AB (input) COMPLEX array, dimension (LDAB,N)
 The upper or lower triangular band matrix A, stored in the first kd+1 rows of the array. The jth column of A is stored in the jth column of the array AB as follows: if UPLO = aqUaq, AB(kd+1+ij,j) = A(i,j) for max(1,jkd)<=i<=j; if UPLO = aqLaq, AB(1+ij,j) = A(i,j) for j<=i<=min(n,j+kd). If DIAG = aqUaq, the diagonal elements of A are not referenced and are assumed to be 1.
 LDAB (input) INTEGER
 The leading dimension of the array AB. LDAB >= KD+1.
 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 ith argument had an illegal value