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zlaqp2.f(3) LAPACK zlaqp2.f(3)

zlaqp2.f -


subroutine zlaqp2 (M, N, OFFSET, A, LDA, JPVT, TAU, VN1, VN2, WORK)
 
ZLAQP2 computes a QR factorization with column pivoting of the matrix block.

ZLAQP2 computes a QR factorization with column pivoting of the matrix block.
Purpose:
 ZLAQP2 computes a QR factorization with column pivoting of
 the block A(OFFSET+1:M,1:N).
 The block A(1:OFFSET,1:N) is accordingly pivoted, but not factorized.
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.
OFFSET
          OFFSET is INTEGER
          The number of rows of the matrix A that must be pivoted
          but no factorized. OFFSET >= 0.
A
          A is COMPLEX*16 array, dimension (LDA,N)
          On entry, the M-by-N matrix A.
          On exit, the upper triangle of block A(OFFSET+1:M,1:N) is
          the triangular factor obtained; the elements in block
          A(OFFSET+1:M,1:N) below the diagonal, together with the
          array TAU, represent the orthogonal matrix Q as a product of
          elementary reflectors. Block A(1:OFFSET,1:N) has been
          accordingly pivoted, but no factorized.
LDA
          LDA is INTEGER
          The leading dimension of the array A. LDA >= max(1,M).
JPVT
          JPVT is INTEGER array, dimension (N)
          On entry, if JPVT(i) .ne. 0, the i-th column of A is permuted
          to the front of A*P (a leading column); if JPVT(i) = 0,
          the i-th column of A is a free column.
          On exit, if JPVT(i) = k, then the i-th column of A*P
          was the k-th column of A.
TAU
          TAU is COMPLEX*16 array, dimension (min(M,N))
          The scalar factors of the elementary reflectors.
VN1
          VN1 is DOUBLE PRECISION array, dimension (N)
          The vector with the partial column norms.
VN2
          VN2 is DOUBLE PRECISION array, dimension (N)
          The vector with the exact column norms.
WORK
          WORK is COMPLEX*16 array, dimension (N)
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
September 2012
Contributors:
G. Quintana-Orti, Depto. de Informatica, Universidad Jaime I, Spain X. Sun, Computer Science Dept., Duke University, USA
 

Partial column norm updating strategy modified on April 2011 Z. Drmac and Z. Bujanovic, Dept. of Mathematics, University of Zagreb, Croatia.
References:
LAPACK Working Note 176
Definition at line 149 of file zlaqp2.f.

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