SRC/dgelqt.f(3)

NAME
SRC/dgelqt.f

SYNOPSIS

  Functions/Subroutines
subroutine dgelqt (m, n, mb, a, lda, t, ldt, work, info)
DGELQT

Function/Subroutine Documentation

  subroutine dgelqt (integer m, integer n, integer mb, double precision, dimension( lda, * ) a, integer lda, double precision, dimension( ldt, * ) t, integer ldt, double precision, dimension( * ) work, integer info)

DGELQT

Purpose:

     DGELQT computes a blocked LQ factorization of a real M-by-N matrix A
     using the compact WY representation of Q.

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.

    MB

              MB is INTEGER
              The block size to be used in the blocked QR.  MIN(M,N) >= MB >= 1.

    A

              A is DOUBLE PRECISION array, dimension (LDA,N)
              On entry, the M-by-N matrix A.
              On exit, the elements on and below the diagonal of the array
              contain the M-by-MIN(M,N) lower trapezoidal matrix L (L is
              lower triangular if M <= N); the elements above the diagonal
              are the rows of V.

    LDA

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

    T

              T is DOUBLE PRECISION array, dimension (LDT,MIN(M,N))
              The upper triangular block reflectors stored in compact form
              as a sequence of upper triangular blocks.  See below
              for further details.

    LDT

              LDT is INTEGER
              The leading dimension of the array T.  LDT >= MB.

    WORK

              WORK is DOUBLE PRECISION array, dimension (MB*N)

    INFO

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

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Further Details:

      The matrix V stores the elementary reflectors H(i) in the i-th row
      above the diagonal. For example, if M=5 and N=3, the matrix V is
                   V = (  1  v1 v1 v1 v1 )
                       (     1  v2 v2 v2 )
                       (         1 v3 v3 )
      where the vi's represent the vectors which define H(i), which are returned
      in the matrix A.  The 1's along the diagonal of V are not stored in A.
      Let K=MIN(M,N).  The number of blocks is B = ceiling(K/MB), where each
      block is of order MB except for the last block, which is of order
      IB = K - (B-1)*MB.  For each of the B blocks, a upper triangular block
      reflector factor is computed: T1, T2, ..., TB.  The MB-by-MB (and IB-by-IB
      for the last block) T's are stored in the MB-by-K matrix T as
                   T = (T1 T2 ... TB).

Definition at line 138 of file dgelqt.f.

Author

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