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SUBROUTINE SORT01( ROWCOL, M, N, U, LDU, WORK, LWORK, RESID )
*
* -- LAPACK test routine (version 3.0) --
* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
* Courant Institute, Argonne National Lab, and Rice University
* February 29, 1992
*
* .. Scalar Arguments ..
CHARACTER ROWCOL
INTEGER LDU, LWORK, M, N
REAL RESID
* ..
* .. Array Arguments ..
REAL U( LDU, * ), WORK( * )
* ..
*
* Purpose
* =======
*
* SORT01 checks that the matrix U is orthogonal by computing the ratio
*
* RESID = norm( I - U*U' ) / ( n * EPS ), if ROWCOL = 'R',
* or
* RESID = norm( I - U'*U ) / ( m * EPS ), if ROWCOL = 'C'.
*
* Alternatively, if there isn't sufficient workspace to form
* I - U*U' or I - U'*U, the ratio is computed as
*
* RESID = abs( I - U*U' ) / ( n * EPS ), if ROWCOL = 'R',
* or
* RESID = abs( I - U'*U ) / ( m * EPS ), if ROWCOL = 'C'.
*
* where EPS is the machine precision. ROWCOL is used only if m = n;
* if m > n, ROWCOL is assumed to be 'C', and if m < n, ROWCOL is
* assumed to be 'R'.
*
* Arguments
* =========
*
* ROWCOL (input) CHARACTER
* Specifies whether the rows or columns of U should be checked
* for orthogonality. Used only if M = N.
* = 'R': Check for orthogonal rows of U
* = 'C': Check for orthogonal columns of U
*
* M (input) INTEGER
* The number of rows of the matrix U.
*
* N (input) INTEGER
* The number of columns of the matrix U.
*
* U (input) REAL array, dimension (LDU,N)
* The orthogonal matrix U. U is checked for orthogonal columns
* if m > n or if m = n and ROWCOL = 'C'. U is checked for
* orthogonal rows if m < n or if m = n and ROWCOL = 'R'.
*
* LDU (input) INTEGER
* The leading dimension of the array U. LDU >= max(1,M).
*
* WORK (workspace) REAL array, dimension (LWORK)
*
* LWORK (input) INTEGER
* The length of the array WORK. For best performance, LWORK
* should be at least N*(N+1) if ROWCOL = 'C' or M*(M+1) if
* ROWCOL = 'R', but the test will be done even if LWORK is 0.
*
* RESID (output) REAL
* RESID = norm( I - U * U' ) / ( n * EPS ), if ROWCOL = 'R', or
* RESID = norm( I - U' * U ) / ( m * EPS ), if ROWCOL = 'C'.
*
* =====================================================================
*
* .. Parameters ..
REAL ZERO, ONE
PARAMETER ( ZERO = 0.0E+0, ONE = 1.0E+0 )
* ..
* .. Local Scalars ..
CHARACTER TRANSU
INTEGER I, J, K, LDWORK, MNMIN
REAL EPS, TMP
* ..
* .. External Functions ..
LOGICAL LSAME
REAL SDOT, SLAMCH, SLANSY
EXTERNAL LSAME, SDOT, SLAMCH, SLANSY
* ..
* .. External Subroutines ..
EXTERNAL SLASET, SSYRK
* ..
* .. Intrinsic Functions ..
INTRINSIC MAX, MIN, REAL
* ..
* .. Executable Statements ..
*
RESID = ZERO
*
* Quick return if possible
*
IF( M.LE.0 .OR. N.LE.0 )
$ RETURN
*
EPS = SLAMCH( 'Precision' )
IF( M.LT.N .OR. ( M.EQ.N .AND. LSAME( ROWCOL, 'R' ) ) ) THEN
TRANSU = 'N'
K = N
ELSE
TRANSU = 'T'
K = M
END IF
MNMIN = MIN( M, N )
*
IF( ( MNMIN+1 )*MNMIN.LE.LWORK ) THEN
LDWORK = MNMIN
ELSE
LDWORK = 0
END IF
IF( LDWORK.GT.0 ) THEN
*
* Compute I - U*U' or I - U'*U.
*
CALL SLASET( 'Upper', MNMIN, MNMIN, ZERO, ONE, WORK, LDWORK )
CALL SSYRK( 'Upper', TRANSU, MNMIN, K, -ONE, U, LDU, ONE, WORK,
$ LDWORK )
*
* Compute norm( I - U*U' ) / ( K * EPS ) .
*
RESID = SLANSY( '1', 'Upper', MNMIN, WORK, LDWORK,
$ WORK( LDWORK*MNMIN+1 ) )
RESID = ( RESID / REAL( K ) ) / EPS
ELSE IF( TRANSU.EQ.'T' ) THEN
*
* Find the maximum element in abs( I - U'*U ) / ( m * EPS )
*
DO 20 J = 1, N
DO 10 I = 1, J
IF( I.NE.J ) THEN
TMP = ZERO
ELSE
TMP = ONE
END IF
TMP = TMP - SDOT( M, U( 1, I ), 1, U( 1, J ), 1 )
RESID = MAX( RESID, ABS( TMP ) )
10 CONTINUE
20 CONTINUE
RESID = ( RESID / REAL( M ) ) / EPS
ELSE
*
* Find the maximum element in abs( I - U*U' ) / ( n * EPS )
*
DO 40 J = 1, M
DO 30 I = 1, J
IF( I.NE.J ) THEN
TMP = ZERO
ELSE
TMP = ONE
END IF
TMP = TMP - SDOT( N, U( J, 1 ), LDU, U( I, 1 ), LDU )
RESID = MAX( RESID, ABS( TMP ) )
30 CONTINUE
40 CONTINUE
RESID = ( RESID / REAL( N ) ) / EPS
END IF
RETURN
*
* End of SORT01
*
END
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