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SUBROUTINE CHST01( N, ILO, IHI, A, LDA, H, LDH, Q, LDQ, WORK,
$ LWORK, RWORK, RESULT )
*
* -- LAPACK test routine (version 3.1) --
* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
* November 2006
*
* .. Scalar Arguments ..
INTEGER IHI, ILO, LDA, LDH, LDQ, LWORK, N
* ..
* .. Array Arguments ..
REAL RESULT( 2 ), RWORK( * )
COMPLEX A( LDA, * ), H( LDH, * ), Q( LDQ, * ),
$ WORK( LWORK )
* ..
*
* Purpose
* =======
*
* CHST01 tests the reduction of a general matrix A to upper Hessenberg
* form: A = Q*H*Q'. Two test ratios are computed;
*
* RESULT(1) = norm( A - Q*H*Q' ) / ( norm(A) * N * EPS )
* RESULT(2) = norm( I - Q'*Q ) / ( N * EPS )
*
* The matrix Q is assumed to be given explicitly as it would be
* following CGEHRD + CUNGHR.
*
* In this version, ILO and IHI are not used, but they could be used
* to save some work if this is desired.
*
* Arguments
* =========
*
* N (input) INTEGER
* The order of the matrix A. N >= 0.
*
* ILO (input) INTEGER
* IHI (input) INTEGER
* A is assumed to be upper triangular in rows and columns
* 1:ILO-1 and IHI+1:N, so Q differs from the identity only in
* rows and columns ILO+1:IHI.
*
* A (input) COMPLEX array, dimension (LDA,N)
* The original n by n matrix A.
*
* LDA (input) INTEGER
* The leading dimension of the array A. LDA >= max(1,N).
*
* H (input) COMPLEX array, dimension (LDH,N)
* The upper Hessenberg matrix H from the reduction A = Q*H*Q'
* as computed by CGEHRD. H is assumed to be zero below the
* first subdiagonal.
*
* LDH (input) INTEGER
* The leading dimension of the array H. LDH >= max(1,N).
*
* Q (input) COMPLEX array, dimension (LDQ,N)
* The orthogonal matrix Q from the reduction A = Q*H*Q' as
* computed by CGEHRD + CUNGHR.
*
* LDQ (input) INTEGER
* The leading dimension of the array Q. LDQ >= max(1,N).
*
* WORK (workspace) COMPLEX array, dimension (LWORK)
*
* LWORK (input) INTEGER
* The length of the array WORK. LWORK >= 2*N*N.
*
* RWORK (workspace) REAL array, dimension (N)
*
* RESULT (output) REAL array, dimension (2)
* RESULT(1) = norm( A - Q*H*Q' ) / ( norm(A) * N * EPS )
* RESULT(2) = norm( I - Q'*Q ) / ( N * EPS )
*
* =====================================================================
*
* .. Parameters ..
REAL ONE, ZERO
PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 )
* ..
* .. Local Scalars ..
INTEGER LDWORK
REAL ANORM, EPS, OVFL, SMLNUM, UNFL, WNORM
* ..
* .. External Functions ..
REAL CLANGE, SLAMCH
EXTERNAL CLANGE, SLAMCH
* ..
* .. External Subroutines ..
EXTERNAL CGEMM, CLACPY, CUNT01, SLABAD
* ..
* .. Intrinsic Functions ..
INTRINSIC CMPLX, MAX, MIN
* ..
* .. Executable Statements ..
*
* Quick return if possible
*
IF( N.LE.0 ) THEN
RESULT( 1 ) = ZERO
RESULT( 2 ) = ZERO
RETURN
END IF
*
UNFL = SLAMCH( 'Safe minimum' )
EPS = SLAMCH( 'Precision' )
OVFL = ONE / UNFL
CALL SLABAD( UNFL, OVFL )
SMLNUM = UNFL*N / EPS
*
* Test 1: Compute norm( A - Q*H*Q' ) / ( norm(A) * N * EPS )
*
* Copy A to WORK
*
LDWORK = MAX( 1, N )
CALL CLACPY( ' ', N, N, A, LDA, WORK, LDWORK )
*
* Compute Q*H
*
CALL CGEMM( 'No transpose', 'No transpose', N, N, N, CMPLX( ONE ),
$ Q, LDQ, H, LDH, CMPLX( ZERO ), WORK( LDWORK*N+1 ),
$ LDWORK )
*
* Compute A - Q*H*Q'
*
CALL CGEMM( 'No transpose', 'Conjugate transpose', N, N, N,
$ CMPLX( -ONE ), WORK( LDWORK*N+1 ), LDWORK, Q, LDQ,
$ CMPLX( ONE ), WORK, LDWORK )
*
ANORM = MAX( CLANGE( '1', N, N, A, LDA, RWORK ), UNFL )
WNORM = CLANGE( '1', N, N, WORK, LDWORK, RWORK )
*
* Note that RESULT(1) cannot overflow and is bounded by 1/(N*EPS)
*
RESULT( 1 ) = MIN( WNORM, ANORM ) / MAX( SMLNUM, ANORM*EPS ) / N
*
* Test 2: Compute norm( I - Q'*Q ) / ( N * EPS )
*
CALL CUNT01( 'Columns', N, N, Q, LDQ, WORK, LWORK, RWORK,
$ RESULT( 2 ) )
*
RETURN
*
* End of CHST01
*
END
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