```      SUBROUTINE DGBEQU( M, N, KL, KU, AB, LDAB, R, C, ROWCND, COLCND,
\$                   AMAX, INFO )
*
*  -- LAPACK routine (version 3.1) --
*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
*     November 2006
*
*     .. Scalar Arguments ..
INTEGER            INFO, KL, KU, LDAB, M, N
DOUBLE PRECISION   AMAX, COLCND, ROWCND
*     ..
*     .. Array Arguments ..
DOUBLE PRECISION   AB( LDAB, * ), C( * ), R( * )
*     ..
*
*  Purpose
*  =======
*
*  DGBEQU computes row and column scalings intended to equilibrate an
*  M-by-N band matrix A and reduce its condition number.  R returns the
*  row scale factors and C the column scale factors, chosen to try to
*  make the largest element in each row and column of the matrix B with
*  elements B(i,j)=R(i)*A(i,j)*C(j) have absolute value 1.
*
*  R(i) and C(j) are restricted to be between SMLNUM = smallest safe
*  number and BIGNUM = largest safe number.  Use of these scaling
*  factors is not guaranteed to reduce the condition number of A but
*  works well in practice.
*
*  Arguments
*  =========
*
*  M       (input) INTEGER
*          The number of rows of the matrix A.  M >= 0.
*
*  N       (input) INTEGER
*          The number of columns 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) DOUBLE PRECISION array, dimension (LDAB,N)
*          The band matrix A, stored in rows 1 to KL+KU+1.  The j-th
*          column of A is stored in the j-th column of the array AB as
*          follows:
*          AB(ku+1+i-j,j) = A(i,j) for max(1,j-ku)<=i<=min(m,j+kl).
*
*  LDAB    (input) INTEGER
*          The leading dimension of the array AB.  LDAB >= KL+KU+1.
*
*  R       (output) DOUBLE PRECISION array, dimension (M)
*          If INFO = 0, or INFO > M, R contains the row scale factors
*          for A.
*
*  C       (output) DOUBLE PRECISION array, dimension (N)
*          If INFO = 0, C contains the column scale factors for A.
*
*  ROWCND  (output) DOUBLE PRECISION
*          If INFO = 0 or INFO > M, ROWCND contains the ratio of the
*          smallest R(i) to the largest R(i).  If ROWCND >= 0.1 and
*          AMAX is neither too large nor too small, it is not worth
*          scaling by R.
*
*  COLCND  (output) DOUBLE PRECISION
*          If INFO = 0, COLCND contains the ratio of the smallest
*          C(i) to the largest C(i).  If COLCND >= 0.1, it is not
*          worth scaling by C.
*
*  AMAX    (output) DOUBLE PRECISION
*          Absolute value of largest matrix element.  If AMAX is very
*          close to overflow or very close to underflow, the matrix
*          should be scaled.
*
*  INFO    (output) INTEGER
*          = 0:  successful exit
*          < 0:  if INFO = -i, the i-th argument had an illegal value
*          > 0:  if INFO = i, and i is
*                <= M:  the i-th row of A is exactly zero
*                >  M:  the (i-M)-th column of A is exactly zero
*
*  =====================================================================
*
*     .. Parameters ..
DOUBLE PRECISION   ONE, ZERO
PARAMETER          ( ONE = 1.0D+0, ZERO = 0.0D+0 )
*     ..
*     .. Local Scalars ..
INTEGER            I, J, KD
DOUBLE PRECISION   BIGNUM, RCMAX, RCMIN, SMLNUM
*     ..
*     .. External Functions ..
DOUBLE PRECISION   DLAMCH
EXTERNAL           DLAMCH
*     ..
*     .. External Subroutines ..
EXTERNAL           XERBLA
*     ..
*     .. Intrinsic Functions ..
INTRINSIC          ABS, MAX, MIN
*     ..
*     .. Executable Statements ..
*
*     Test the input parameters
*
INFO = 0
IF( M.LT.0 ) 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.KL+KU+1 ) THEN
INFO = -6
END IF
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'DGBEQU', -INFO )
RETURN
END IF
*
*     Quick return if possible
*
IF( M.EQ.0 .OR. N.EQ.0 ) THEN
ROWCND = ONE
COLCND = ONE
AMAX = ZERO
RETURN
END IF
*
*     Get machine constants.
*
SMLNUM = DLAMCH( 'S' )
BIGNUM = ONE / SMLNUM
*
*     Compute row scale factors.
*
DO 10 I = 1, M
R( I ) = ZERO
10 CONTINUE
*
*     Find the maximum element in each row.
*
KD = KU + 1
DO 30 J = 1, N
DO 20 I = MAX( J-KU, 1 ), MIN( J+KL, M )
R( I ) = MAX( R( I ), ABS( AB( KD+I-J, J ) ) )
20    CONTINUE
30 CONTINUE
*
*     Find the maximum and minimum scale factors.
*
RCMIN = BIGNUM
RCMAX = ZERO
DO 40 I = 1, M
RCMAX = MAX( RCMAX, R( I ) )
RCMIN = MIN( RCMIN, R( I ) )
40 CONTINUE
AMAX = RCMAX
*
IF( RCMIN.EQ.ZERO ) THEN
*
*        Find the first zero scale factor and return an error code.
*
DO 50 I = 1, M
IF( R( I ).EQ.ZERO ) THEN
INFO = I
RETURN
END IF
50    CONTINUE
ELSE
*
*        Invert the scale factors.
*
DO 60 I = 1, M
R( I ) = ONE / MIN( MAX( R( I ), SMLNUM ), BIGNUM )
60    CONTINUE
*
*        Compute ROWCND = min(R(I)) / max(R(I))
*
ROWCND = MAX( RCMIN, SMLNUM ) / MIN( RCMAX, BIGNUM )
END IF
*
*     Compute column scale factors
*
DO 70 J = 1, N
C( J ) = ZERO
70 CONTINUE
*
*     Find the maximum element in each column,
*     assuming the row scaling computed above.
*
KD = KU + 1
DO 90 J = 1, N
DO 80 I = MAX( J-KU, 1 ), MIN( J+KL, M )
C( J ) = MAX( C( J ), ABS( AB( KD+I-J, J ) )*R( I ) )
80    CONTINUE
90 CONTINUE
*
*     Find the maximum and minimum scale factors.
*
RCMIN = BIGNUM
RCMAX = ZERO
DO 100 J = 1, N
RCMIN = MIN( RCMIN, C( J ) )
RCMAX = MAX( RCMAX, C( J ) )
100 CONTINUE
*
IF( RCMIN.EQ.ZERO ) THEN
*
*        Find the first zero scale factor and return an error code.
*
DO 110 J = 1, N
IF( C( J ).EQ.ZERO ) THEN
INFO = M + J
RETURN
END IF
110    CONTINUE
ELSE
*
*        Invert the scale factors.
*
DO 120 J = 1, N
C( J ) = ONE / MIN( MAX( C( J ), SMLNUM ), BIGNUM )
120    CONTINUE
*
*        Compute COLCND = min(C(J)) / max(C(J))
*
COLCND = MAX( RCMIN, SMLNUM ) / MIN( RCMAX, BIGNUM )
END IF
*
RETURN
*
*     End of DGBEQU
*
END

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