/*  -- translated by f2c (version 20191129).
   You must link the resulting object file with libf2c:
	on Microsoft Windows system, link with libf2c.lib;
	on Linux or Unix systems, link with .../path/to/libf2c.a -lm
	or, if you install libf2c.a in a standard place, with -lf2c -lm
	-- in that order, at the end of the command line, as in
		cc *.o -lf2c -lm
	Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,

		http://www.netlib.org/f2c/libf2c.zip
*/

#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   
   > Download DLASSQ + dependencies   
   > <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlassq.
f">   
   > [TGZ]</a>   
   > <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlassq.
f">   
   > [ZIP]</a>   
   > <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlassq.
f">   
   > [TXT]</a>   
   > \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_ */

