forked from lijiext/lammps
169 lines
4.7 KiB
FortranFixed
169 lines
4.7 KiB
FortranFixed
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*> \brief \b ZLASSQ updates a sum of squares represented in scaled form.
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*
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* =========== DOCUMENTATION ===========
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*
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* Online html documentation available at
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* http://www.netlib.org/lapack/explore-html/
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*
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*> \htmlonly
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*> Download ZLASSQ + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/zlassq.f">
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*> [TGZ]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/zlassq.f">
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*> [ZIP]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/zlassq.f">
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*> [TXT]</a>
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*> \endhtmlonly
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*
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* Definition:
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* ===========
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*
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* SUBROUTINE ZLASSQ( N, X, INCX, SCALE, SUMSQ )
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*
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* .. Scalar Arguments ..
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* INTEGER INCX, N
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* DOUBLE PRECISION SCALE, SUMSQ
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* ..
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* .. Array Arguments ..
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* COMPLEX*16 X( * )
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* ..
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*
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*
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*> \par Purpose:
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* =============
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*>
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*> \verbatim
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*>
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*> ZLASSQ returns the values scl and ssq such that
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*>
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*> ( scl**2 )*ssq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq,
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*>
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*> where x( i ) = abs( X( 1 + ( i - 1 )*INCX ) ). The value of sumsq is
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*> assumed to be at least unity and the value of ssq will then satisfy
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*>
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*> 1.0 .le. ssq .le. ( sumsq + 2*n ).
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*>
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*> scale is assumed to be non-negative and scl returns the value
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*>
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*> scl = max( scale, abs( real( x( i ) ) ), abs( aimag( x( i ) ) ) ),
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*> i
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*>
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*> scale and sumsq must be supplied in SCALE and SUMSQ respectively.
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*> SCALE and SUMSQ are overwritten by scl and ssq respectively.
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*>
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*> The routine makes only one pass through the vector X.
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*> \endverbatim
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*
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* Arguments:
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* ==========
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*
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*> \param[in] N
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*> \verbatim
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*> N is INTEGER
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*> The number of elements to be used from the vector X.
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*> \endverbatim
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*>
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*> \param[in] X
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*> \verbatim
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*> X is COMPLEX*16 array, dimension (N)
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*> The vector x as described above.
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*> x( i ) = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.
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*> \endverbatim
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*>
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*> \param[in] INCX
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*> \verbatim
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*> INCX is INTEGER
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*> The increment between successive values of the vector X.
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*> INCX > 0.
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*> \endverbatim
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*>
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*> \param[in,out] SCALE
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*> \verbatim
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*> SCALE is DOUBLE PRECISION
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*> On entry, the value scale in the equation above.
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*> On exit, SCALE is overwritten with the value scl .
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*> \endverbatim
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*>
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*> \param[in,out] SUMSQ
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*> \verbatim
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*> SUMSQ is DOUBLE PRECISION
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*> On entry, the value sumsq in the equation above.
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*> On exit, SUMSQ is overwritten with the value ssq .
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*> \endverbatim
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*
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* Authors:
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* ========
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*
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*> \author Univ. of Tennessee
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*> \author Univ. of California Berkeley
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*> \author Univ. of Colorado Denver
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*> \author NAG Ltd.
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*
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*> \date September 2012
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*
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*> \ingroup complex16OTHERauxiliary
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*
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* =====================================================================
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SUBROUTINE ZLASSQ( N, X, INCX, SCALE, SUMSQ )
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*
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* -- LAPACK auxiliary routine (version 3.4.2) --
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* -- LAPACK is a software package provided by Univ. of Tennessee, --
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* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
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* September 2012
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*
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* .. Scalar Arguments ..
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INTEGER INCX, N
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DOUBLE PRECISION SCALE, SUMSQ
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* ..
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* .. Array Arguments ..
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COMPLEX*16 X( * )
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* ..
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*
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* =====================================================================
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*
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* .. Parameters ..
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DOUBLE PRECISION ZERO
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PARAMETER ( ZERO = 0.0D+0 )
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* ..
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* .. Local Scalars ..
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INTEGER IX
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DOUBLE PRECISION TEMP1
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* ..
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* .. External Functions ..
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LOGICAL DISNAN
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EXTERNAL DISNAN
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC ABS, DBLE, DIMAG
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* ..
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* .. Executable Statements ..
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*
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IF( N.GT.0 ) THEN
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DO 10 IX = 1, 1 + ( N-1 )*INCX, INCX
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TEMP1 = ABS( DBLE( X( IX ) ) )
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IF( TEMP1.GT.ZERO.OR.DISNAN( TEMP1 ) ) THEN
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IF( SCALE.LT.TEMP1 ) THEN
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SUMSQ = 1 + SUMSQ*( SCALE / TEMP1 )**2
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SCALE = TEMP1
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ELSE
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SUMSQ = SUMSQ + ( TEMP1 / SCALE )**2
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END IF
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END IF
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TEMP1 = ABS( DIMAG( X( IX ) ) )
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IF( TEMP1.GT.ZERO.OR.DISNAN( TEMP1 ) ) THEN
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IF( SCALE.LT.TEMP1 ) THEN
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SUMSQ = 1 + SUMSQ*( SCALE / TEMP1 )**2
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SCALE = TEMP1
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ELSE
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SUMSQ = SUMSQ + ( TEMP1 / SCALE )**2
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END IF
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END IF
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10 CONTINUE
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END IF
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*
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RETURN
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*
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* End of ZLASSQ
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*
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END
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