SRC/zgbequb.f(3)           Library Functions Manual           SRC/zgbequb.f(3)

NAME
       SRC/zgbequb.f

SYNOPSIS
   Functions/Subroutines
       subroutine zgbequb (m, n, kl, ku, ab, ldab, r, c, rowcnd, colcnd, amax,
           info)
           ZGBEQUB

Function/Subroutine Documentation
   subroutine zgbequb (integer m, integer n, integer kl, integer ku,
       complex*16, dimension( ldab, * ) ab, integer ldab, double precision,
       dimension( * ) r, double precision, dimension( * ) c, double precision
       rowcnd, double precision colcnd, double precision amax, integer info)
       ZGBEQUB

       Purpose:


            ZGBEQUB computes row and column scalings intended to equilibrate an
            M-by-N 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 an absolute value of at most
            the radix.

            R(i) and C(j) are restricted to be a power of the radix 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.

            This routine differs from ZGEEQU by restricting the scaling factors
            to a power of the radix.  Barring over- and underflow, scaling by
            these factors introduces no additional rounding errors.  However, the
            scaled entries' magnitudes are no longer approximately 1 but lie
            between sqrt(radix) and 1/sqrt(radix).

       Parameters
           M

                     M is INTEGER
                     The number of rows of the matrix A.  M >= 0.

           N

                     N is INTEGER
                     The number of columns of the matrix A.  N >= 0.

           KL

                     KL is INTEGER
                     The number of subdiagonals within the band of A.  KL >= 0.

           KU

                     KU is INTEGER
                     The number of superdiagonals within the band of A.  KU >= 0.

           AB

                     AB is COMPLEX*16 array, dimension (LDAB,N)
                     On entry, the matrix A in band storage, 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(N,j+kl)

           LDAB

                     LDAB is INTEGER
                     The leading dimension of the array A.  LDAB >= max(1,M).

           R

                     R is DOUBLE PRECISION array, dimension (M)
                     If INFO = 0 or INFO > M, R contains the row scale factors
                     for A.

           C

                     C is DOUBLE PRECISION array, dimension (N)
                     If INFO = 0,  C contains the column scale factors for A.

           ROWCND

                     ROWCND is 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

                     COLCND is 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

                     AMAX is 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

                     INFO is 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

       Author
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Definition at line 159 of file zgbequb.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

LAPACK                          Version 3.12.0                SRC/zgbequb.f(3)