STBCON(3)                  MathKeisan LAPACK routine                 STBCON(3)



NAME
       STBCON  -  the  reciprocal of the condition number of a triangular band
       matrix A, in either the 1-norm or the infinity-norm

SYNOPSIS
       SUBROUTINE STBCON( NORM, UPLO, DIAG, N,  KD,  AB,  LDAB,  RCOND,  WORK,
                          IWORK, INFO )

           CHARACTER      DIAG, NORM, UPLO

           INTEGER        INFO, KD, LDAB, N

           REAL           RCOND

           INTEGER        IWORK( * )

           REAL           AB( LDAB, * ), WORK( * )

PURPOSE
       STBCON estimates the reciprocal of the condition number of a triangular
       band matrix A, in either the 1-norm or the infinity-norm.

       The norm of A is computed and an estimate is obtained for norm(inv(A)),
       then the reciprocal of the condition number is computed as
          RCOND = 1 / ( norm(A) * norm(inv(A)) ).


ARGUMENTS
       NORM    (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.

       UPLO    (input) CHARACTER*1
               = 'U':  A is upper triangular;
               = 'L':  A is lower triangular.

       DIAG    (input) CHARACTER*1
               = 'N':  A is non-unit triangular;
               = 'U':  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) REAL array, dimension (LDAB,N)
               The  upper  or  lower  triangular  band matrix A, stored in the
               first kd+1 rows of the array. The j-th column of A is stored in
               the  j-th  column  of  the  array AB as follows: if UPLO = 'U',
               AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j; if UPLO  =  'L',
               AB(1+i-j,j)     = A(i,j) for j<=i<=min(n,j+kd).  If DIAG = 'U',
               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, com-
               puted as RCOND = 1/(norm(A) * norm(inv(A))).

       WORK    (workspace) REAL array, dimension (3*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



 LAPACK routine (version 3.1)    November 2006                       STBCON(3)