DGBBRD(3)      LAPACK routine of NEC Numeric Library Collection      DGBBRD(3)



NAME
       DGBBRD

SYNOPSIS
       SUBROUTINE DGBBRD (VECT, M, N, NCC, KL, KU, AB, LDAB, D, E, Q, LDQ, PT,
           LDPT, C, LDC, WORK, INFO)



PURPOSE
            DGBBRD reduces a real general m-by-n band matrix A to upper
            bidiagonal form B by an orthogonal transformation: Q**T * A * P = B.

            The routine computes B, and optionally forms Q or P**T, or computes
            Q**T*C for a given matrix C.




ARGUMENTS
           VECT      (input)
                     VECT is CHARACTER*1
                     Specifies whether or not the matrices Q and P**T are to be
                     formed.
                     = 'N': do not form Q or P**T;
                     = 'Q': form Q only;
                     = 'P': form P**T only;
                     = 'B': form both.

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

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

           NCC       (input)
                     NCC is INTEGER
                     The number of columns of the matrix C.  NCC >= 0.

           KL        (input)
                     KL is INTEGER
                     The number of subdiagonals of the matrix A. KL >= 0.

           KU        (input)
                     KU is INTEGER
                     The number of superdiagonals of the matrix A. KU >= 0.

           AB        (input/output)
                     AB is DOUBLE PRECISION array, dimension (LDAB,N)
                     On entry, the m-by-n 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).
                     On exit, A is overwritten by values generated during the
                     reduction.

           LDAB      (input)
                     LDAB is INTEGER
                     The leading dimension of the array A. LDAB >= KL+KU+1.

           D         (output)
                     D is DOUBLE PRECISION array, dimension (min(M,N))
                     The diagonal elements of the bidiagonal matrix B.

           E         (output)
                     E is DOUBLE PRECISION array, dimension (min(M,N)-1)
                     The superdiagonal elements of the bidiagonal matrix B.

           Q         (output)
                     Q is DOUBLE PRECISION array, dimension (LDQ,M)
                     If VECT = 'Q' or 'B', the m-by-m orthogonal matrix Q.
                     If VECT = 'N' or 'P', the array Q is not referenced.

           LDQ       (input)
                     LDQ is INTEGER
                     The leading dimension of the array Q.
                     LDQ >= max(1,M) if VECT = 'Q' or 'B'; LDQ >= 1 otherwise.

           PT        (output)
                     PT is DOUBLE PRECISION array, dimension (LDPT,N)
                     If VECT = 'P' or 'B', the n-by-n orthogonal matrix P'.
                     If VECT = 'N' or 'Q', the array PT is not referenced.

           LDPT      (input)
                     LDPT is INTEGER
                     The leading dimension of the array PT.
                     LDPT >= max(1,N) if VECT = 'P' or 'B'; LDPT >= 1 otherwise.

           C         (input/output)
                     C is DOUBLE PRECISION array, dimension (LDC,NCC)
                     On entry, an m-by-ncc matrix C.
                     On exit, C is overwritten by Q**T*C.
                     C is not referenced if NCC = 0.

           LDC       (input)
                     LDC is INTEGER
                     The leading dimension of the array C.
                     LDC >= max(1,M) if NCC > 0; LDC >= 1 if NCC = 0.

           WORK      (output)
                     WORK is DOUBLE PRECISION array, dimension (2*max(M,N))

           INFO      (output)
                     INFO is INTEGER
                     = 0:  successful exit.
                     < 0:  if INFO = -i, the i-th argument had an illegal value.



LAPACK routine                  31 October 2017                      DGBBRD(3)