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NAME
     spbcon - estimate the reciprocal of the condition number (in
     the  1-norm)  of  a  real  symmetric  positive definite band
     matrix using the Cholesky factorization A = U**T*U  or  A  =
     L*L**T computed by SPBTRF

SYNOPSIS
     SUBROUTINE SPBCON( UPLO, N,  KD,  AB,  LDAB,  ANORM,  RCOND,
               WORK, IWORK, INFO )

     CHARACTER UPLO

     INTEGER INFO, KD, LDAB, N

     REAL ANORM, RCOND

     INTEGER IWORK( * )

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



     #include <sunperf.h>

     void spbcon(char uplo, int n, int kd, float *sab, int  ldab,
               float anorm, float *srcond, int *info);

PURPOSE
     SPBCON estimates the reciprocal of the condition number  (in
     the  1-norm)  of  a  real  symmetric  positive definite band
     matrix using the Cholesky factorization A = U**T*U  or  A  =
     L*L**T computed by SPBTRF.

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


ARGUMENTS
     UPLO      (input) CHARACTER*1
               = 'U':  Upper triangular factor stored in AB;
               = 'L':  Lower triangular factor stored in AB.

     N         (input) INTEGER
               The order of the matrix A.  N >= 0.

     KD        (input) INTEGER
               The number of superdiagonals of the  matrix  A  if
               UPLO  = 'U', or the number of subdiagonals if UPLO
               = 'L'.  KD >= 0.

     AB        (input) REAL array, dimension (LDAB,N)
               The triangular factor U or  L  from  the  Cholesky
               factorization A = U**T*U or A = L*L**T of the band
               matrix A, stored in the first  KD+1  rows  of  the
               array.  The j-th column of U or L is stored in the
               j-th column of the array AB as follows:   if  UPLO
               ='U',   AB(kd+1+i-j,j)   =   U(i,j)  for  max(1,j-
               kd)<=i<=j; if UPLO ='L', AB(1+i-j,j)     =  L(i,j)
               for j<=i<=min(n,j+kd).

     LDAB      (input) INTEGER
               The leading dimension of the array  AB.   LDAB  >=
               KD+1.

     ANORM     (input) REAL
               The 1-norm (or  infinity-norm)  of  the  symmetric
               band matrix A.

     RCOND     (output) REAL
               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) 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 ille-
               gal value

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