```      SUBROUTINE SGBCON( NORM, N, KL, KU, AB, LDAB, IPIV, ANORM, RCOND,
\$                   WORK, IWORK, INFO )
*
*  -- LAPACK routine (version 3.1) --
*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
*     November 2006
*
*     Modified to call SLACN2 in place of SLACON, 7 Feb 03, SJH.
*
*     .. Scalar Arguments ..
CHARACTER          NORM
INTEGER            INFO, KL, KU, LDAB, N
REAL               ANORM, RCOND
*     ..
*     .. Array Arguments ..
INTEGER            IPIV( * ), IWORK( * )
REAL               AB( LDAB, * ), WORK( * )
*     ..
*
*  Purpose
*  =======
*
*  SGBCON estimates the reciprocal of the condition number of a real
*  general band matrix A, in either the 1-norm or the infinity-norm,
*  using the LU factorization computed by SGBTRF.
*
*  An estimate is obtained for norm(inv(A)), and 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.
*
*  N       (input) INTEGER
*          The order of the matrix A.  N >= 0.
*
*  KL      (input) INTEGER
*          The number of subdiagonals within the band of A.  KL >= 0.
*
*  KU      (input) INTEGER
*          The number of superdiagonals within the band of A.  KU >= 0.
*
*  AB      (input) REAL array, dimension (LDAB,N)
*          Details of the LU factorization of the band matrix A, as
*          computed by SGBTRF.  U is stored as an upper triangular band
*          matrix with KL+KU superdiagonals in rows 1 to KL+KU+1, and
*          the multipliers used during the factorization are stored in
*          rows KL+KU+2 to 2*KL+KU+1.
*
*  LDAB    (input) INTEGER
*          The leading dimension of the array AB.  LDAB >= 2*KL+KU+1.
*
*  IPIV    (input) INTEGER array, dimension (N)
*          The pivot indices; for 1 <= i <= N, row i of the matrix was
*          interchanged with row IPIV(i).
*
*  ANORM   (input) REAL
*          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) REAL
*          The reciprocal of the condition number of the matrix A,
*          computed 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
*
*  =====================================================================
*
*     .. Parameters ..
REAL               ONE, ZERO
PARAMETER          ( ONE = 1.0E+0, ZERO = 0.0E+0 )
*     ..
*     .. Local Scalars ..
LOGICAL            LNOTI, ONENRM
CHARACTER          NORMIN
INTEGER            IX, J, JP, KASE, KASE1, KD, LM
REAL               AINVNM, SCALE, SMLNUM, T
*     ..
*     .. Local Arrays ..
INTEGER            ISAVE( 3 )
*     ..
*     .. External Functions ..
LOGICAL            LSAME
INTEGER            ISAMAX
REAL               SDOT, SLAMCH
EXTERNAL           LSAME, ISAMAX, SDOT, SLAMCH
*     ..
*     .. External Subroutines ..
EXTERNAL           SAXPY, SLACN2, SLATBS, SRSCL, XERBLA
*     ..
*     .. Intrinsic Functions ..
INTRINSIC          ABS, MIN
*     ..
*     .. Executable Statements ..
*
*     Test the input parameters.
*
INFO = 0
ONENRM = NORM.EQ.'1' .OR. LSAME( NORM, 'O' )
IF( .NOT.ONENRM .AND. .NOT.LSAME( NORM, 'I' ) ) THEN
INFO = -1
ELSE IF( N.LT.0 ) THEN
INFO = -2
ELSE IF( KL.LT.0 ) THEN
INFO = -3
ELSE IF( KU.LT.0 ) THEN
INFO = -4
ELSE IF( LDAB.LT.2*KL+KU+1 ) THEN
INFO = -6
ELSE IF( ANORM.LT.ZERO ) THEN
INFO = -8
END IF
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'SGBCON', -INFO )
RETURN
END IF
*
*     Quick return if possible
*
RCOND = ZERO
IF( N.EQ.0 ) THEN
RCOND = ONE
RETURN
ELSE IF( ANORM.EQ.ZERO ) THEN
RETURN
END IF
*
SMLNUM = SLAMCH( 'Safe minimum' )
*
*     Estimate the norm of inv(A).
*
AINVNM = ZERO
NORMIN = 'N'
IF( ONENRM ) THEN
KASE1 = 1
ELSE
KASE1 = 2
END IF
KD = KL + KU + 1
LNOTI = KL.GT.0
KASE = 0
10 CONTINUE
CALL SLACN2( N, WORK( N+1 ), WORK, IWORK, AINVNM, KASE, ISAVE )
IF( KASE.NE.0 ) THEN
IF( KASE.EQ.KASE1 ) THEN
*
*           Multiply by inv(L).
*
IF( LNOTI ) THEN
DO 20 J = 1, N - 1
LM = MIN( KL, N-J )
JP = IPIV( J )
T = WORK( JP )
IF( JP.NE.J ) THEN
WORK( JP ) = WORK( J )
WORK( J ) = T
END IF
CALL SAXPY( LM, -T, AB( KD+1, J ), 1, WORK( J+1 ), 1 )
20          CONTINUE
END IF
*
*           Multiply by inv(U).
*
CALL SLATBS( 'Upper', 'No transpose', 'Non-unit', NORMIN, N,
\$                   KL+KU, AB, LDAB, WORK, SCALE, WORK( 2*N+1 ),
\$                   INFO )
ELSE
*
*           Multiply by inv(U').
*
CALL SLATBS( 'Upper', 'Transpose', 'Non-unit', NORMIN, N,
\$                   KL+KU, AB, LDAB, WORK, SCALE, WORK( 2*N+1 ),
\$                   INFO )
*
*           Multiply by inv(L').
*
IF( LNOTI ) THEN
DO 30 J = N - 1, 1, -1
LM = MIN( KL, N-J )
WORK( J ) = WORK( J ) - SDOT( LM, AB( KD+1, J ), 1,
\$                        WORK( J+1 ), 1 )
JP = IPIV( J )
IF( JP.NE.J ) THEN
T = WORK( JP )
WORK( JP ) = WORK( J )
WORK( J ) = T
END IF
30          CONTINUE
END IF
END IF
*
*        Divide X by 1/SCALE if doing so will not cause overflow.
*
NORMIN = 'Y'
IF( SCALE.NE.ONE ) THEN
IX = ISAMAX( N, WORK, 1 )
IF( SCALE.LT.ABS( WORK( IX ) )*SMLNUM .OR. SCALE.EQ.ZERO )
\$         GO TO 40
CALL SRSCL( N, SCALE, WORK, 1 )
END IF
GO TO 10
END IF
*
*     Compute the estimate of the reciprocal condition number.
*
IF( AINVNM.NE.ZERO )
\$   RCOND = ( ONE / AINVNM ) / ANORM
*
40 CONTINUE
RETURN
*
*     End of SGBCON
*
END

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