cungtr.f −

**Functions/Subroutines**

subroutine **cungtr** (UPLO, N, A, LDA, TAU, WORK, LWORK, INFO)

CUNGTR

**subroutine cungtr (characterUPLO, integerN, complex, dimension( lda, * )A, integerLDA, complex, dimension( * )TAU, complex, dimension( * )WORK, integerLWORK, integerINFO)
CUNGTR**

**Purpose:**

CUNGTR generates a complex unitary matrix Q which is defined as the

product of n-1 elementary reflectors of order N, as returned by

CHETRD:

if UPLO = ’U’, Q = H(n-1) . . . H(2) H(1),

if UPLO = ’L’, Q = H(1) H(2) . . . H(n-1).

**Parameters:**

*UPLO*

UPLO is CHARACTER*1

= ’U’: Upper triangle of A contains elementary reflectors

from CHETRD;

= ’L’: Lower triangle of A contains elementary reflectors

from CHETRD.

*N*

N is INTEGER

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

*A*

A is COMPLEX array, dimension (LDA,N)

On entry, the vectors which define the elementary reflectors,

as returned by CHETRD.

On exit, the N-by-N unitary matrix Q.

*LDA*

LDA is INTEGER

The leading dimension of the array A. LDA >= N.

*TAU*

TAU is COMPLEX array, dimension (N-1)

TAU(i) must contain the scalar factor of the elementary

reflector H(i), as returned by CHETRD.

*WORK*

WORK is COMPLEX 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 >= N-1.

For optimum performance LWORK >= (N-1)*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:**

November 2011

Definition at line 124 of file cungtr.f.

Generated automatically by Doxygen for LAPACK from the source code.