DGEQLF (3)  Linux Manuals
NAME
dgeqlf.f 
SYNOPSIS
Functions/Subroutines
subroutine dgeqlf (M, N, A, LDA, TAU, WORK, LWORK, INFO)
DGEQLF
Function/Subroutine Documentation
subroutine dgeqlf (integerM, integerN, double precision, dimension( lda, * )A, integerLDA, double precision, dimension( * )TAU, double precision, dimension( * )WORK, integerLWORK, integerINFO)
DGEQLF
Purpose:

DGEQLF computes a QL factorization of a real MbyN matrix A: A = Q * L.
Parameters:

M
M is INTEGER The number of rows of the matrix A. M >= 0.
NN is INTEGER The number of columns of the matrix A. N >= 0.
AA is DOUBLE PRECISION array, dimension (LDA,N) On entry, the MbyN matrix A. On exit, if m >= n, the lower triangle of the subarray A(mn+1:m,1:n) contains the NbyN lower triangular matrix L; if m <= n, the elements on and below the (nm)th superdiagonal contain the MbyN 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).
LDALDA is INTEGER The leading dimension of the array A. LDA >= max(1,M).
TAUTAU is DOUBLE PRECISION array, dimension (min(M,N)) The scalar factors of the elementary reflectors (see Further Details).
WORKWORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK)) On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
LWORKLWORK is INTEGER The dimension of the array WORK. LWORK >= max(1,N). For optimum performance LWORK >= N*NB, where NB is the optimal blocksize. 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.
INFOINFO is INTEGER = 0: successful exit < 0: if INFO = i, the ith argument had an illegal value
Author:

Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
 November 2011
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**T where tau is a real scalar, and v is a real vector with v(mk+i+1:m) = 0 and v(mk+i) = 1; v(1:mk+i1) is stored on exit in A(1:mk+i1,nk+i), and tau in TAU(i).
Definition at line 139 of file dgeqlf.f.
Author
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