cungtr(3)

NAME

CUNGTR - generate a complex unitary matrix Q which is de

fined as the product of n-1 elementary reflectors of order N, as

returned by CHETRD

SYNOPSIS

SUBROUTINE CUNGTR( UPLO, N, A, LDA, TAU, WORK, LWORK, INFO
)
    CHARACTER      UPLO
    INTEGER        INFO, LDA, LWORK, N
    COMPLEX        A( LDA, * ), TAU( * ), WORK( * )

PURPOSE

CUNGTR generates a complex unitary matrix Q which is de

fined 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).

ARGUMENTS

UPLO (input) CHARACTER*1

= 'U': Upper triangle of A contains elementary re

flectors from CHETRD; = 'L': Lower triangle of A contains elemen

tary reflectors from CHETRD.

N (input) INTEGER

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

A (input/output) 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 (input) INTEGER

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

TAU (input) COMPLEX array, dimension (N-1)

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

mentary reflector H(i), as returned by CHETRD.

WORK (workspace/output) COMPLEX array, dimension

(LWORK)

On exit, if INFO = 0, WORK(1) returns the optimal

LWORK.

LWORK (input) INTEGER

The dimension of the array WORK. LWORK >= N-1.

For optimum performance LWORK >= (N-1)*NB, where NB is the opti

mal 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 (output) INTEGER

= 0: successful exit
< 0: if INFO = -i, the i-th argument had an ille

gal value

LAPACK version 3.0 15 June 2000

CUNGTR(3)