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*> \brief \b CLASSQ updates a sum of squares represented in scaled form.
*
* =========== DOCUMENTATION ===========
*
* Online html documentation available at
* http://www.netlib.org/lapack/explore-html/
*
*> \htmlonly
*> Download CLASSQ + dependencies
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/classq.f">
*> [TGZ]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/classq.f">
*> [ZIP]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/classq.f">
*> [TXT]</a>
*> \endhtmlonly
*
* Definition:
* ===========
*
* SUBROUTINE CLASSQ( N, X, INCX, SCALE, SUMSQ )
*
* .. Scalar Arguments ..
* INTEGER INCX, N
* REAL SCALE, SUMSQ
* ..
* .. Array Arguments ..
* COMPLEX X( * )
* ..
*
*
*> \par Purpose:
* =============
*>
*> \verbatim
*>
*> CLASSQ returns the values scl and ssq such that
*>
*> ( scl**2 )*ssq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq,
*>
*> where x( i ) = abs( X( 1 + ( i - 1 )*INCX ) ). The value of sumsq is
*> assumed to be at least unity and the value of ssq will then satisfy
*>
*> 1.0 <= ssq <= ( sumsq + 2*n ).
*>
*> scale is assumed to be non-negative and scl returns the value
*>
*> scl = max( scale, abs( real( x( i ) ) ), abs( aimag( x( i ) ) ) ),
*> i
*>
*> scale and sumsq must be supplied in SCALE and SUMSQ respectively.
*> SCALE and SUMSQ are overwritten by scl and ssq respectively.
*>
*> The routine makes only one pass through the vector X.
*> \endverbatim
*
* Arguments:
* ==========
*
*> \param[in] N
*> \verbatim
*> N is INTEGER
*> The number of elements to be used from the vector X.
*> \endverbatim
*>
*> \param[in] X
*> \verbatim
*> X is COMPLEX array, dimension (1+(N-1)*INCX)
*> The vector x as described above.
*> x( i ) = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.
*> \endverbatim
*>
*> \param[in] INCX
*> \verbatim
*> INCX is INTEGER
*> The increment between successive values of the vector X.
*> INCX > 0.
*> \endverbatim
*>
*> \param[in,out] SCALE
*> \verbatim
*> SCALE is REAL
*> On entry, the value scale in the equation above.
*> On exit, SCALE is overwritten with the value scl .
*> \endverbatim
*>
*> \param[in,out] SUMSQ
*> \verbatim
*> SUMSQ is REAL
*> On entry, the value sumsq in the equation above.
*> On exit, SUMSQ is overwritten with the value ssq .
*> \endverbatim
*
* Authors:
* ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \date December 2016
*
*> \ingroup complexOTHERauxiliary
*
* =====================================================================
SUBROUTINE CLASSQ( N, X, INCX, SCALE, SUMSQ )
*
* -- LAPACK auxiliary routine (version 3.7.0) --
* -- LAPACK is a software package provided by Univ. of Tennessee, --
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
* December 2016
*
* .. Scalar Arguments ..
INTEGER INCX, N
REAL SCALE, SUMSQ
* ..
* .. Array Arguments ..
COMPLEX X( * )
* ..
*
* =====================================================================
*
* .. Parameters ..
REAL ZERO
PARAMETER ( ZERO = 0.0E+0 )
* ..
* .. Local Scalars ..
INTEGER IX
REAL TEMP1
* ..
* .. External Functions ..
LOGICAL SISNAN
EXTERNAL SISNAN
* ..
* .. Intrinsic Functions ..
INTRINSIC ABS, AIMAG, REAL
* ..
* .. Executable Statements ..
*
IF( N.GT.0 ) THEN
DO 10 IX = 1, 1 + ( N-1 )*INCX, INCX
TEMP1 = ABS( REAL( X( IX ) ) )
IF( TEMP1.GT.ZERO.OR.SISNAN( TEMP1 ) ) THEN
IF( SCALE.LT.TEMP1 ) THEN
SUMSQ = 1 + SUMSQ*( SCALE / TEMP1 )**2
SCALE = TEMP1
ELSE
SUMSQ = SUMSQ + ( TEMP1 / SCALE )**2
END IF
END IF
TEMP1 = ABS( AIMAG( X( IX ) ) )
IF( TEMP1.GT.ZERO.OR.SISNAN( TEMP1 ) ) THEN
IF( SCALE.LT.TEMP1 .OR. SISNAN( TEMP1 ) ) THEN
SUMSQ = 1 + SUMSQ*( SCALE / TEMP1 )**2
SCALE = TEMP1
ELSE
SUMSQ = SUMSQ + ( TEMP1 / SCALE )**2
END IF
END IF
10 CONTINUE
END IF
*
RETURN
*
* End of CLASSQ
*
END
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