claswlq.f

Section: LAPACK (3)
Updated: Tue Nov 14 2017
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NAME

claswlq.f  

SYNOPSIS


 

Functions/Subroutines


subroutine claswlq (M, N, MB, NB, A, LDA, T, LDT, WORK, LWORK, INFO)
 

Function/Subroutine Documentation

 

subroutine claswlq (integer M, integer N, integer MB, integer NB, complex, dimension( lda, * ) A, integer LDA, complex, dimension( ldt, *) T, integer LDT, complex, dimension( * ) WORK, integer LWORK, integer INFO)

Purpose:

CLASWLQ computes a blocked Short-Wide LQ factorization of a M-by-N matrix A, where N >= M: A = L * 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 >= M >= 0.


MB

          MB is INTEGER
          The row block size to be used in the blocked QR.
          M >= MB >= 1


 
NB

          NB is INTEGER
          The column block size to be used in the blocked QR.
          NB > M.


A

          A is COMPLEX 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 N-by-N lower triangular matrix L;
          the elements above the diagonal represent Q by the rows
          of blocked V (see Further Details).


LDA

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


T

          T is COMPLEX array,
          dimension (LDT, N * Number_of_row_blocks)
          where Number_of_row_blocks = CEIL((N-M)/(NB-M))
          The blocked upper triangular block reflectors stored in compact form
          as a sequence of upper triangular blocks.
          See Further Details below.


LDT

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


WORK

         (workspace) COMPLEX array, dimension (MAX(1,LWORK))


 
LWORK

          The dimension of the array WORK.  LWORK >= MB*M.
          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

          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:

Short-Wide LQ (SWLQ) performs LQ by a sequence of orthogonal transformations, representing Q as a product of other orthogonal matrices Q = Q(1) * Q(2) * . . . * Q(k) where each Q(i) zeros out upper diagonal entries of a block of NB rows of A: Q(1) zeros out the upper diagonal entries of rows 1:NB of A Q(2) zeros out the bottom MB-N rows of rows [1:M,NB+1:2*NB-M] of A Q(3) zeros out the bottom MB-N rows of rows [1:M,2*NB-M+1:3*NB-2*M] of A . . .

Q(1) is computed by GELQT, which represents Q(1) by Householder vectors stored under the diagonal of rows 1:MB of A, and by upper triangular block reflectors, stored in array T(1:LDT,1:N). For more information see Further Details in GELQT.

Q(i) for i>1 is computed by TPLQT, which represents Q(i) by Householder vectors stored in columns [(i-1)*(NB-M)+M+1:i*(NB-M)+M] of A, and by upper triangular block reflectors, stored in array T(1:LDT,(i-1)*M+1:i*M). The last Q(k) may use fewer rows. For more information see Further Details in TPQRT.

For more details of the overall algorithm, see the description of Sequential TSQR in Section 2.2 of [1].

[1] “Communication-Optimal Parallel and Sequential QR and LU Factorizations,” J. Demmel, L. Grigori, M. Hoemmen, J. Langou, SIAM J. Sci. Comput, vol. 34, no. 1, 2012

Definition at line 152 of file claswlq.f.  

Author

Generated automatically by Doxygen for LAPACK from the source code.


 

Index

NAME
SYNOPSIS
Functions/Subroutines
Function/Subroutine Documentation
subroutine claswlq (integer M, integer N, integer MB, integer NB, complex, dimension( lda, * ) A, integer LDA, complex, dimension( ldt, *) T, integer LDT, complex, dimension( * ) WORK, integer LWORK, integer INFO)
Author