cungtr-f(3)

cungtr.f –

Synopsis

Functions/Subroutines

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

Function/Subroutine Documentation

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

 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.

Author

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