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*> \brief \b CLARGE
*
* =========== DOCUMENTATION ===========
*
* Online html documentation available at
* http://www.netlib.org/lapack/explore-html/
*
* Definition:
* ===========
*
* SUBROUTINE CLARGE( N, A, LDA, ISEED, WORK, INFO )
*
* .. Scalar Arguments ..
* INTEGER INFO, LDA, N
* ..
* .. Array Arguments ..
* INTEGER ISEED( 4 )
* COMPLEX A( LDA, * ), WORK( * )
* ..
*
*
*> \par Purpose:
* =============
*>
*> \verbatim
*>
*> CLARGE pre- and post-multiplies a complex general n by n matrix A
*> with a random unitary matrix: A = U*D*U'.
*> \endverbatim
*
* Arguments:
* ==========
*
*> \param[in] N
*> \verbatim
*> N is INTEGER
*> The order of the matrix A. N >= 0.
*> \endverbatim
*>
*> \param[in,out] A
*> \verbatim
*> A is COMPLEX array, dimension (LDA,N)
*> On entry, the original n by n matrix A.
*> On exit, A is overwritten by U*A*U' for some random
*> unitary matrix U.
*> \endverbatim
*>
*> \param[in] LDA
*> \verbatim
*> LDA is INTEGER
*> The leading dimension of the array A. LDA >= N.
*> \endverbatim
*>
*> \param[in,out] ISEED
*> \verbatim
*> ISEED is INTEGER array, dimension (4)
*> On entry, the seed of the random number generator; the array
*> elements must be between 0 and 4095, and ISEED(4) must be
*> odd.
*> On exit, the seed is updated.
*> \endverbatim
*>
*> \param[out] WORK
*> \verbatim
*> WORK is COMPLEX array, dimension (2*N)
*> \endverbatim
*>
*> \param[out] INFO
*> \verbatim
*> INFO is INTEGER
*> = 0: successful exit
*> < 0: if INFO = -i, the i-th argument had an illegal value
*> \endverbatim
*
* Authors:
* ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \date November 2011
*
*> \ingroup complex_matgen
*
* =====================================================================
SUBROUTINE CLARGE( N, A, LDA, ISEED, WORK, INFO )
*
* -- LAPACK auxiliary routine (version 3.4.0) --
* -- LAPACK is a software package provided by Univ. of Tennessee, --
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
* November 2011
*
* .. Scalar Arguments ..
INTEGER INFO, LDA, N
* ..
* .. Array Arguments ..
INTEGER ISEED( 4 )
COMPLEX A( LDA, * ), WORK( * )
* ..
*
* =====================================================================
*
* .. Parameters ..
COMPLEX ZERO, ONE
PARAMETER ( ZERO = ( 0.0E+0, 0.0E+0 ),
$ ONE = ( 1.0E+0, 0.0E+0 ) )
* ..
* .. Local Scalars ..
INTEGER I
REAL WN
COMPLEX TAU, WA, WB
* ..
* .. External Subroutines ..
EXTERNAL CGEMV, CGERC, CLARNV, CSCAL, XERBLA
* ..
* .. Intrinsic Functions ..
INTRINSIC ABS, MAX, REAL
* ..
* .. External Functions ..
REAL SCNRM2
EXTERNAL SCNRM2
* ..
* .. Executable Statements ..
*
* Test the input arguments
*
INFO = 0
IF( N.LT.0 ) THEN
INFO = -1
ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
INFO = -3
END IF
IF( INFO.LT.0 ) THEN
CALL XERBLA( 'CLARGE', -INFO )
RETURN
END IF
*
* pre- and post-multiply A by random unitary matrix
*
DO 10 I = N, 1, -1
*
* generate random reflection
*
CALL CLARNV( 3, ISEED, N-I+1, WORK )
WN = SCNRM2( N-I+1, WORK, 1 )
WA = ( WN / ABS( WORK( 1 ) ) )*WORK( 1 )
IF( WN.EQ.ZERO ) THEN
TAU = ZERO
ELSE
WB = WORK( 1 ) + WA
CALL CSCAL( N-I, ONE / WB, WORK( 2 ), 1 )
WORK( 1 ) = ONE
TAU = REAL( WB / WA )
END IF
*
* multiply A(i:n,1:n) by random reflection from the left
*
CALL CGEMV( 'Conjugate transpose', N-I+1, N, ONE, A( I, 1 ),
$ LDA, WORK, 1, ZERO, WORK( N+1 ), 1 )
CALL CGERC( N-I+1, N, -TAU, WORK, 1, WORK( N+1 ), 1, A( I, 1 ),
$ LDA )
*
* multiply A(1:n,i:n) by random reflection from the right
*
CALL CGEMV( 'No transpose', N, N-I+1, ONE, A( 1, I ), LDA,
$ WORK, 1, ZERO, WORK( N+1 ), 1 )
CALL CGERC( N, N-I+1, -TAU, WORK( N+1 ), 1, WORK, 1, A( 1, I ),
$ LDA )
10 CONTINUE
RETURN
*
* End of CLARGE
*
END
|
