# zungbr.f man page

zungbr.f —

## Synopsis

### Functions/Subroutines

subroutinezungbr(VECT, M, N, K, A, LDA, TAU, WORK, LWORK, INFO)ZUNGBR

## Function/Subroutine Documentation

### subroutine zungbr (characterVECT, integerM, integerN, integerK, complex*16, dimension( lda, * )A, integerLDA, complex*16, dimension( * )TAU, complex*16, dimension( * )WORK, integerLWORK, integerINFO)

**ZUNGBR**

**Purpose:**

```
ZUNGBR generates one of the complex unitary matrices Q or P**H
determined by ZGEBRD when reducing a complex matrix A to bidiagonal
form: A = Q * B * P**H. Q and P**H are defined as products of
elementary reflectors H(i) or G(i) respectively.
If VECT = 'Q', A is assumed to have been an M-by-K matrix, and Q
is of order M:
if m >= k, Q = H(1) H(2) . . . H(k) and ZUNGBR returns the first n
columns of Q, where m >= n >= k;
if m < k, Q = H(1) H(2) . . . H(m-1) and ZUNGBR returns Q as an
M-by-M matrix.
If VECT = 'P', A is assumed to have been a K-by-N matrix, and P**H
is of order N:
if k < n, P**H = G(k) . . . G(2) G(1) and ZUNGBR returns the first m
rows of P**H, where n >= m >= k;
if k >= n, P**H = G(n-1) . . . G(2) G(1) and ZUNGBR returns P**H as
an N-by-N matrix.
```

**Parameters:**

*VECT*

```
VECT is CHARACTER*1
Specifies whether the matrix Q or the matrix P**H is
required, as defined in the transformation applied by ZGEBRD:
= 'Q': generate Q;
= 'P': generate P**H.
```

*M*

```
M is INTEGER
The number of rows of the matrix Q or P**H to be returned.
M >= 0.
```

*N*

```
N is INTEGER
The number of columns of the matrix Q or P**H to be returned.
N >= 0.
If VECT = 'Q', M >= N >= min(M,K);
if VECT = 'P', N >= M >= min(N,K).
```

*K*

```
K is INTEGER
If VECT = 'Q', the number of columns in the original M-by-K
matrix reduced by ZGEBRD.
If VECT = 'P', the number of rows in the original K-by-N
matrix reduced by ZGEBRD.
K >= 0.
```

*A*

```
A is COMPLEX*16 array, dimension (LDA,N)
On entry, the vectors which define the elementary reflectors,
as returned by ZGEBRD.
On exit, the M-by-N matrix Q or P**H.
```

*LDA*

```
LDA is INTEGER
The leading dimension of the array A. LDA >= M.
```

*TAU*

```
TAU is COMPLEX*16 array, dimension
(min(M,K)) if VECT = 'Q'
(min(N,K)) if VECT = 'P'
TAU(i) must contain the scalar factor of the elementary
reflector H(i) or G(i), which determines Q or P**H, as
returned by ZGEBRD in its array argument TAUQ or TAUP.
```

*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 >= max(1,min(M,N)).
For optimum performance LWORK >= min(M,N)*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

Definition at line 158 of file zungbr.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

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