dgeqrf man page on Scientific

Printed from http://www.polarhome.com/service/man/?qf=dgeqrf&af=0&tf=2&of=Scientific

DGEQRF(1)		 LAPACK routine (version 3.2)		     DGEQRF(1)

NAME
       DGEQRF - computes a QR factorization of a real M-by-N matrix A

SYNOPSIS
       SUBROUTINE DGEQRF( M, N, A, LDA, TAU, WORK, LWORK, INFO )

	   INTEGER	  INFO, LDA, LWORK, M, N

	   DOUBLE	  PRECISION A( LDA, * ), TAU( * ), WORK( * )

PURPOSE
       DGEQRF  computes	 a QR factorization of a real M-by-N matrix A: A = Q *
       R.

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, the  elements  on  and
	       above the diagonal of the array contain the min(M,N)-by-N upper
	       trapezoidal matrix R (R is upper triangular if  m  >=  n);  the
	       elements	 below the diagonal, with the array TAU, represent the
	       orthogonal matrix Q as a product of min(m,n) elementary reflec‐
	       tors (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,    dimension
       (MAX(1,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 opti‐
	       mum performance LWORK >= N*NB, where NB is the  optimal	block‐
	       size.   If  LWORK  = -1, then a workspace query is assumed; the
	       routine only calculates the optimal size	 of  the  WORK	array,
	       returns this value as the first entry of the WORK array, and no
	       error message related to LWORK is issued by XERBLA.

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

FURTHER DETAILS
       The matrix Q is represented as a product of elementary reflectors
	  Q = H(1) H(2) . . . H(k), 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(1:i-1) = 0 and v(i) = 1; v(i+1:m) is stored on	 exit  in  A(i+1:m,i),
       and tau in TAU(i).

 LAPACK routine (version 3.2)	 November 2008			     DGEQRF(1)
[top]

List of man pages available for Scientific

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Tweet
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
....................................................................
Vote for polarhome
Free Shell Accounts :: the biggest list on the net