dtzrzf.f man page

dtzrzf.f —

Synopsis

Functions/Subroutines

subroutine dtzrzf (M, N, A, LDA, TAU, WORK, LWORK, INFO)
DTZRZF

Function/Subroutine Documentation

subroutine dtzrzf (integerM, integerN, double precision, dimension( lda, * )A, integerLDA, double precision, dimension( * )TAU, double precision, dimension( * )WORK, integerLWORK, integerINFO)

DTZRZF

Purpose:

DTZRZF reduces the M-by-N ( M<=N ) real upper trapezoidal matrix A
to upper triangular form by means of orthogonal transformations.

The upper trapezoidal matrix A is factored as

   A = ( R  0 ) * Z,

where Z is an N-by-N orthogonal matrix and R is an M-by-M upper
triangular matrix.

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.

A

A is DOUBLE PRECISION array, dimension (LDA,N)
On entry, the leading M-by-N upper trapezoidal part of the
array A must contain the matrix to be factorized.
On exit, the leading M-by-M upper triangular part of A
contains the upper triangular matrix R, and elements M+1 to
N of the first M rows of A, with the array TAU, represent the
orthogonal matrix Z as a product of M elementary reflectors.

LDA

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

TAU

TAU is DOUBLE PRECISION array, dimension (M)
The scalar factors of the elementary reflectors.

WORK

WORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK))
On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

LWORK

LWORK is INTEGER
The dimension of the array WORK.  LWORK >= max(1,M).
For optimum performance LWORK >= M*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.

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.

Date:

April 2012

Contributors:

A. Petitet, Computer Science Dept., Univ. of Tenn., Knoxville, USA

Further Details:

The N-by-N matrix Z can be computed by

   Z =  Z(1)*Z(2)* ... *Z(M)

where each N-by-N Z(k) is given by

   Z(k) = I - tau(k)*v(k)*v(k)**T

with v(k) is the kth row vector of the M-by-N matrix

   V = ( I   A(:,M+1:N) )

I is the M-by-M identity matrix, A(:,M+1:N) 
is the output stored in A on exit from DTZRZF,
and tau(k) is the kth element of the array TAU.

Definition at line 152 of file dtzrzf.f.

Author

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Referenced By

dtzrzf(3) is an alias of dtzrzf.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK