Heh. That's not a technical term. You can do something like this:

for $i (0 .. $npts-1) {
   for $j ($i+1 .. $npts-1) {
      $dx = $x[$j] - $x[$i];
      $dy = $y[$j] - $y[$i];
      $d = sqrt($dx*$dx + $dy*$dy);
      $f = $d - $distance[$i][$j];
      $fx[$i] += $f * $dx / $d;
      $fy[$i] += $f * $dy / $d;
      $fx[$j] -= $f * $dx / $d;
      $fy[$j] -= $f * $dy / $d;
   }
}

[download]

That gives you the x and y components of the total "force" on each point. Then you can update the positions.

for $i (0 .. $npts-1) {
   $x[$i] += $dt * $fx[$i];
   $y[$i] += $dt * $fy[$i];
}

[download]

The trick is choosing a good time step $dt. Too small and it will converge very slowly. Too high and it will rattle around and never settle down. (You might want to look at the forces before choosing a time step, which is why I've put the update in a separate loop.) This kind of thing is sensitive to initial conditions and doesn't always converge well, so you may need to fiddle around with it to get it to work.

In reply to Re^3: Data visualisation. by Anonymous Monk
in thread Data visualisation. by BrowserUk

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