/* -- translated by f2c (version 20100827).
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*/
#include "f2c.h"
/* > \brief \b DLASSQ updates a sum of squares represented in scaled form.
=========== DOCUMENTATION ===========
Online html documentation available at
http://www.netlib.org/lapack/explore-html/
> \htmlonly
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> \endhtmlonly
Definition:
===========
SUBROUTINE DLASSQ( N, X, INCX, SCALE, SUMSQ )
INTEGER INCX, N
DOUBLE PRECISION SCALE, SUMSQ
DOUBLE PRECISION X( * )
> \par Purpose:
=============
>
> \verbatim
>
> DLASSQ returns the values scl and smsq such that
>
> ( scl**2 )*smsq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq,
>
> where x( i ) = X( 1 + ( i - 1 )*INCX ). The value of sumsq is
> assumed to be non-negative and scl returns the value
>
> scl = max( scale, abs( x( i ) ) ).
>
> scale and sumsq must be supplied in SCALE and SUMSQ and
> scl and smsq are overwritten on SCALE and SUMSQ 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 DOUBLE PRECISION array, dimension (N)
> The vector for which a scaled sum of squares is computed.
> 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 DOUBLE PRECISION
> On entry, the value scale in the equation above.
> On exit, SCALE is overwritten with scl , the scaling factor
> for the sum of squares.
> \endverbatim
>
> \param[in,out] SUMSQ
> \verbatim
> SUMSQ is DOUBLE PRECISION
> On entry, the value sumsq in the equation above.
> On exit, SUMSQ is overwritten with smsq , the basic sum of
> squares from which scl has been factored out.
> \endverbatim
Authors:
========
> \author Univ. of Tennessee
> \author Univ. of California Berkeley
> \author Univ. of Colorado Denver
> \author NAG Ltd.
> \date September 2012
> \ingroup auxOTHERauxiliary
=====================================================================
Subroutine */ int igraphdlassq_(integer *n, doublereal *x, integer *incx,
doublereal *scale, doublereal *sumsq)
{
/* System generated locals */
integer i__1, i__2;
doublereal d__1;
/* Local variables */
integer ix;
doublereal absxi;
extern logical igraphdisnan_(doublereal *);
/* -- LAPACK auxiliary routine (version 3.4.2) --
-- LAPACK is a software package provided by Univ. of Tennessee, --
-- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
September 2012
=====================================================================
Parameter adjustments */
--x;
/* Function Body */
if (*n > 0) {
i__1 = (*n - 1) * *incx + 1;
i__2 = *incx;
for (ix = 1; i__2 < 0 ? ix >= i__1 : ix <= i__1; ix += i__2) {
absxi = (d__1 = x[ix], abs(d__1));
if (absxi > 0. || igraphdisnan_(&absxi)) {
if (*scale < absxi) {
/* Computing 2nd power */
d__1 = *scale / absxi;
*sumsq = *sumsq * (d__1 * d__1) + 1;
*scale = absxi;
} else {
/* Computing 2nd power */
d__1 = absxi / *scale;
*sumsq += d__1 * d__1;
}
}
/* L10: */
}
}
return 0;
/* End of DLASSQ */
} /* igraphdlassq_ */