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Subject: RE: Not clear to understand :)
Date: Thu, 22 Nov 2007 11:40:00 -0000
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From: <keith.briggs@bt.com>
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These are *not* equivalent in floating point, of course.  The first is bett=
er.=20=20=20
Even better:

  for (i =3D 1; i <=3D n; i++)
    {
      m_x +=3D (x[i * xstride] - m_x) / i;
      m_y +=3D (y[i * ystride] - m_y) / i;
    }

Keith

-----Original Message-----
From: gsl-discuss-owner@sourceware.org
[mailto:gsl-discuss-owner@sourceware.org]On Behalf Of Serhiy Lisovenko
Sent: 22 November 2007 11:34
To: gsl-discuss@sourceware.org
Subject: Not clear to understand :)


in file fit/linear.c

  for (i =3D 0; i < n; i++)
    {
      m_x +=3D (x[i * xstride] - m_x) / (i + 1.0);
      m_y +=3D (y[i * ystride] - m_y) / (i + 1.0);
    }

and other same...

code equivalent to

  for (i =3D 0; i < n; i++)
    {
      m_x +=3Dx[i * xstride];
      m_y +=3Dy[i * ystride];
    }
m_x/=3D(double)n;
m_y/=3D(double)n;

But the second code is more clear and some faster (no extra divisions).