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SUBROUTINE ZUPGTR( UPLO, N, AP, TAU, Q, LDQ, WORK, INFO )
*
* -- LAPACK routine (version 3.2) --
* -- LAPACK is a software package provided by Univ. of Tennessee, --
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
* November 2006
*
* .. Scalar Arguments ..
CHARACTER UPLO
INTEGER INFO, LDQ, N
* ..
* .. Array Arguments ..
COMPLEX*16 AP( * ), Q( LDQ, * ), TAU( * ), WORK( * )
* ..
*
* Purpose
* =======
*
* ZUPGTR generates a complex unitary matrix Q which is defined as the
* product of n-1 elementary reflectors H(i) of order n, as returned by
* ZHPTRD using packed storage:
*
* 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 triangular packed storage used in previous
* call to ZHPTRD;
* = 'L': Lower triangular packed storage used in previous
* call to ZHPTRD.
*
* N (input) INTEGER
* The order of the matrix Q. N >= 0.
*
* AP (input) COMPLEX*16 array, dimension (N*(N+1)/2)
* The vectors which define the elementary reflectors, as
* returned by ZHPTRD.
*
* TAU (input) COMPLEX*16 array, dimension (N-1)
* TAU(i) must contain the scalar factor of the elementary
* reflector H(i), as returned by ZHPTRD.
*
* Q (output) COMPLEX*16 array, dimension (LDQ,N)
* The N-by-N unitary matrix Q.
*
* LDQ (input) INTEGER
* The leading dimension of the array Q. LDQ >= max(1,N).
*
* WORK (workspace) COMPLEX*16 array, dimension (N-1)
*
* INFO (output) INTEGER
* = 0: successful exit
* < 0: if INFO = -i, the i-th argument had an illegal value
*
* =====================================================================
*
* .. Parameters ..
COMPLEX*16 CZERO, CONE
PARAMETER ( CZERO = ( 0.0D+0, 0.0D+0 ),
$ CONE = ( 1.0D+0, 0.0D+0 ) )
* ..
* .. Local Scalars ..
LOGICAL UPPER
INTEGER I, IINFO, IJ, J
* ..
* .. External Functions ..
LOGICAL LSAME
EXTERNAL LSAME
* ..
* .. External Subroutines ..
EXTERNAL XERBLA, ZUNG2L, ZUNG2R
* ..
* .. Intrinsic Functions ..
INTRINSIC MAX
* ..
* .. Executable Statements ..
*
* Test the input arguments
*
INFO = 0
UPPER = LSAME( UPLO, 'U' )
IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
INFO = -1
ELSE IF( N.LT.0 ) THEN
INFO = -2
ELSE IF( LDQ.LT.MAX( 1, N ) ) THEN
INFO = -6
END IF
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'ZUPGTR', -INFO )
RETURN
END IF
*
* Quick return if possible
*
IF( N.EQ.0 )
$ RETURN
*
IF( UPPER ) THEN
*
* Q was determined by a call to ZHPTRD with UPLO = 'U'
*
* Unpack the vectors which define the elementary reflectors and
* set the last row and column of Q equal to those of the unit
* matrix
*
IJ = 2
DO 20 J = 1, N - 1
DO 10 I = 1, J - 1
Q( I, J ) = AP( IJ )
IJ = IJ + 1
10 CONTINUE
IJ = IJ + 2
Q( N, J ) = CZERO
20 CONTINUE
DO 30 I = 1, N - 1
Q( I, N ) = CZERO
30 CONTINUE
Q( N, N ) = CONE
*
* Generate Q(1:n-1,1:n-1)
*
CALL ZUNG2L( N-1, N-1, N-1, Q, LDQ, TAU, WORK, IINFO )
*
ELSE
*
* Q was determined by a call to ZHPTRD with UPLO = 'L'.
*
* Unpack the vectors which define the elementary reflectors and
* set the first row and column of Q equal to those of the unit
* matrix
*
Q( 1, 1 ) = CONE
DO 40 I = 2, N
Q( I, 1 ) = CZERO
40 CONTINUE
IJ = 3
DO 60 J = 2, N
Q( 1, J ) = CZERO
DO 50 I = J + 1, N
Q( I, J ) = AP( IJ )
IJ = IJ + 1
50 CONTINUE
IJ = IJ + 2
60 CONTINUE
IF( N.GT.1 ) THEN
*
* Generate Q(2:n,2:n)
*
CALL ZUNG2R( N-1, N-1, N-1, Q( 2, 2 ), LDQ, TAU, WORK,
$ IINFO )
END IF
END IF
RETURN
*
* End of ZUPGTR
*
END
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