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dgeqlf (3)
  • >> dgeqlf (3) ( Solaris man: Библиотечные вызовы )
  • 
    NAME
         dgeqlf - compute a QL factorization of a real M-by-N  matrix
         A
    
    SYNOPSIS
         SUBROUTINE DGEQLF( M, N, A, LDA, TAU, WORK, LWORK, INFO )
    
         INTEGER INFO, LDA, LWORK, M, N
    
         DOUBLE PRECISION A( LDA, * ), TAU( * ), WORK( LWORK )
    
    
    
         #include <sunperf.h>
    
         void dgeqlf(int m, int n, double *da, int lda, double  *tau,
                   int *info) ;
    
    PURPOSE
         DGEQLF computes a QL factorization of a real  M-by-N  matrix
         A:  A = Q * L.
    
    
    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.
    
         A         (input/output) DOUBLE PRECISION  array,  dimension
                   (LDA,N)
                   On entry, the M-by-N matrix A.  On exit, if  m  >=
                   n,   the  lower  triangle  of  the  subarray  A(m-
                   n+1:m,1:n) contains the  N-by-N  lower  triangular
                   matrix L; if m <= n, the elements on and below the
                   (n-m)-th superdiagonal contain  the  M-by-N  lower
                   trapezoidal matrix L; the remaining elements, with
                   the array TAU, represent the orthogonal  matrix  Q
                   as a product of elementary reflectors (see Further
                   Details).  LDA      (input)  INTEGER  The  leading
                   dimension of the array A.  LDA >= max(1,M).
    
         TAU       (output)   DOUBLE   PRECISION   array,   dimension
                   (min(M,N))
                   The scalar factors of  the  elementary  reflectors
                   (see Further Details).
    
         WORK      (workspace/output) DOUBLE PRECISION array,  dimen-
                   sion (LWORK)
                   On exit, if INFO = 0, WORK(1) returns the  optimal
                   LWORK.
    
         LWORK     (input) INTEGER
                   The  dimension  of  the  array  WORK.   LWORK   >=
                   max(1,N).   For optimum performance LWORK >= N*NB,
                   where NB is the optimal blocksize.
    
         INFO      (output) INTEGER
                   = 0:  successful exit
                   < 0:  if INFO = -i, the i-th argument had an ille-
                   gal value
    
    FURTHER DETAILS
         The matrix Q is  represented  as  a  product  of  elementary
         reflectors
    
            Q = H(k) . . . H(2) H(1), where k = min(m,n).
    
         Each H(i) has the form
    
            H(i) = I - tau * v * v'
    
         where tau is a real scalar, and v is a real vector with
         v(m-k+i+1:m) = 0 and v(m-k+i) = 1; v(1:m-k+i-1) is stored on
         exit in A(1:m-k+i-1,n-k+i), and tau in TAU(i).
    
    
    
    


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