# zunghr.f(3) [debian man page]

```zunghr.f(3)							      LAPACK							       zunghr.f(3)

NAME
zunghr.f -

SYNOPSIS
Functions/Subroutines
subroutine zunghr (N, ILO, IHI, A, LDA, TAU, WORK, LWORK, INFO)
ZUNGHR

Function/Subroutine Documentation
subroutine zunghr (integerN, integerILO, integerIHI, complex*16, dimension( lda, * )A, integerLDA, complex*16, dimension( * )TAU, complex*16,
dimension( * )WORK, integerLWORK, integerINFO)
ZUNGHR

Purpose:

ZUNGHR generates a complex unitary matrix Q which is defined as the
product of IHI-ILO elementary reflectors of order N, as returned by
ZGEHRD:

Q = H(ilo) H(ilo+1) . . . H(ihi-1).

Parameters:
N

N is INTEGER
The order of the matrix Q. N >= 0.

ILO

ILO is INTEGER

IHI

IHI is INTEGER

ILO and IHI must have the same values as in the previous call
of ZGEHRD. Q is equal to the unit matrix except in the
submatrix Q(ilo+1:ihi,ilo+1:ihi).
1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.

A

A is COMPLEX*16 array, dimension (LDA,N)
On entry, the vectors which define the elementary reflectors,
as returned by ZGEHRD.
On exit, the N-by-N unitary matrix Q.

LDA

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

TAU

TAU is COMPLEX*16 array, dimension (N-1)
TAU(i) must contain the scalar factor of the elementary
reflector H(i), as returned by ZGEHRD.

WORK

WORK is COMPLEX*16 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 >= IHI-ILO.
For optimum performance LWORK >= (IHI-ILO)*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

NAG Ltd.

Date:
November 2011

Definition at line 127 of file zunghr.f.

Author
Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.1							  Sun May 26 2013						       zunghr.f(3)```

## Check Out this Related Man Page

```ZUNGHR(l)								 )								 ZUNGHR(l)

NAME
ZUNGHR  -  generate  a complex unitary matrix Q which is defined as the product of IHI-ILO elementary reflectors of order N, as returned by
ZGEHRD

SYNOPSIS
SUBROUTINE ZUNGHR( N, ILO, IHI, A, LDA, TAU, WORK, LWORK, INFO )

INTEGER	  IHI, ILO, INFO, LDA, LWORK, N

COMPLEX*16	  A( LDA, * ), TAU( * ), WORK( * )

PURPOSE
ZUNGHR generates a complex unitary matrix Q which is defined as the product of IHI-ILO elementary reflectors of order  N,  as  returned	by
ZGEHRD: Q = H(ilo) H(ilo+1) . . . H(ihi-1).

ARGUMENTS
N       (input) INTEGER
The order of the matrix Q. N >= 0.

ILO     (input) INTEGER
IHI	(input)  INTEGER  ILO  and  IHI must have the same values as in the previous call of ZGEHRD. Q is equal to the unit matrix
except in the submatrix Q(ilo+1:ihi,ilo+1:ihi).	1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.

A       (input/output) COMPLEX*16 array, dimension (LDA,N)
On entry, the vectors which define the elementary reflectors, as returned by ZGEHRD.  On exit, the N-by-N unitary matrix Q.

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

TAU     (input) COMPLEX*16 array, dimension (N-1)
TAU(i) must contain the scalar factor of the elementary reflector H(i), as returned by ZGEHRD.

WORK    (workspace/output) COMPLEX*16 array, dimension (LWORK)
On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

LWORK   (input) INTEGER
The dimension of the array WORK. LWORK >= IHI-ILO.  For optimum performance LWORK >= (IHI-ILO)*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

LAPACK version 3.0						   15 June 2000 							 ZUNGHR(l)```
Man Page