kNNI and WeNNI has hard coded small numbers, change to something standardized.

[Jari Häkkinen]

source:trunk/yat/utility/kNNI.cc​ at approximately line 73:

double d=(distance[*k].second ? distance[*k].second : 1e-10);

and source:trunk/yat/utility/WeNNI.cc​ at approximately line 66:

double d=(distance[*k].second ? distance[*k].second : 1e-10);

[Markus Ringnér]

std::numeric_limits<double>::epsilon() should perhaps be used?

[Peter]

Well, if we look at how d in WeNNi for example

...
  // Avoid division with zero (perfect match vectors)
  double d=(distance[*k].second ? distance[*k].second : 1e-10);
  new_value+=(weight_(distance[*k].first,j) *
  data_(distance[*k].first,j)/d);
  norm+=weight_(distance[*k].first,j)/d;
}
// No impute if no contributions from neighbours.
if (norm){
  imputed_data_raw_(i,j) = new_value/norm;
  new_value+=(weight_(distance[*k].first,j) * data_(distance[*k].first,j)/d);
  norm+=weight_(distance[*k].first,j)/d;
...

we see that d is set to a small number to avoid division by zero. So we want d to be small but not too small because then "new_value/norm" will result in Inf divided by Inf or worse if only one of norm and new_value becomes Inf. How can we avoid that? std::numeric_limits<double>::epsilon() does not really do the work here. Because epsilon is defined as the difference between 1.0 and next represented number. In other words, what epsilon is the smallest number you can add to 1.0 without getting back 1.0. I can't see the connection to when you wanna divide by a small number and avoid hitting the ceiling. I'm not an expert in floating point representation, but the latter must depend on your range in exponent wehereas the epsilon tells you about precision in the Mantissa (?).

[Jari Häkkinen]

Reading through ​http://www.bnikolic.co.uk/blog/cpp-rr-epsilon.html I think we should use Markus suggestion of std::numeric_limits<double>::epsilon(). The number is small enough to not matter too much but large enough to avoid infinities.

[Jari Häkkinen]

(In [1554]) Fixes #192. Using std::numeric_limits, since impute algorithms are slightly changed template results also changes.