# zunghr.f - Man Page

SRC/zunghr.f

## Synopsis

### Functions/Subroutines

subroutine zunghr (n, ilo, ihi, a, lda, tau, work, lwork, info)
ZUNGHR

## Function/Subroutine Documentation

### subroutine zunghr (integer n, integer ilo, integer ihi, complex*16, dimension( lda, * ) a, integer lda, complex*16, dimension( * ) tau, complex*16, dimension( * ) work, integer lwork, integer info)

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.

Definition at line 125 of file zunghr.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page zunghr(3) is an alias of zunghr.f(3).

Tue Nov 28 2023 12:08:42 Version 3.12.0 LAPACK