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

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

     CHARACTER DIAG, NORM, UPLO

     INTEGER INFO, KD, LDAB, N

     DOUBLE PRECISION RCOND

     INTEGER IWORK( * )

     DOUBLE PRECISION AB( LDAB, * ), WORK( * )



     #include <sunperf.h>

     void dtbcon(char norm, char uplo, char diag, int n, int  kd,
               double  *dab, int ldab, double *drcond, int *info)
               ;

PURPOSE
     DTBCON 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) DOUBLE PRECISION 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) DOUBLE PRECISION
               The reciprocal of  the  condition  number  of  the
               matrix   A,  computed  as  RCOND  =  1/(norm(A)  *
               norm(inv(A))).

     WORK      (workspace)  DOUBLE  PRECISION  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 ille-
               gal value

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