Re: [PATCH 8/8] diff: improve positioning of add/delete blocks in diffs

[Michael Haggerty <mhagger@alum.mit.edu>]

On 08/04/2016 02:04 AM, Stefan Beller wrote:
> On Wed, Aug 3, 2016 at 4:30 PM, Michael Haggerty <mhagger@alum.mit.edu> wrote:
>> Stefan Beller wrote:
>>> [...]
>>> Rather the 10 describes the ratio of "advanced magic" to pure indentation
>>> based scoring in my understanding.
>>
>> No, it's basically just a number against which the other constants are
>> compared. E.g., if another bonus wants to balance out against exactly
>> one space of indentation, its constant needs to be 10. If it wants to
>> balance out against exactly 5 spaces, its constant needs to be 50. Etc.
> 
> So another interpretation is that the 10 gives the resolution for all other
> constants, i.e. if we keep 10, then we can only give weights in 1/10 of
> "one indent". But the "ideal" weight may not be a multiple of 1/10,
> so we approximate them to the nearest multiple of 1/10.
> 
> If we were to use 1000 here, we could have a higher accuracy of the
> other constants, but probably we do not care about the 3rd decimal place
> for these because they are created heuristically from a corpus that may
> not warrant a precision of constants with a 3rd decimal place.

Not only that. Since all of the inputs to the heuristic are integers,
the outputs are discontinuous and can take only certain discrete values.
And the outputs are only ever compared against one another. So a small
adjustment to the output will only make a difference if it causes the
value to become larger/smaller than another of the possible output
values. So too high a resolution makes no sense at all.

That being said, I didn't actually check in any systematic way whether
the resolution of 10:1 is high enough in practice. But I can say that
the overall performance of the heuristic (in terms of number of errors
counted) remained constant over a relatively large parameter range, so I
think the resolution is sufficient.

Feel free to play with the parameters and/or other heuristics. The tools
and raw data are all published in [1]. Let me know if you need help
getting started.

Michael

[1] https://github.com/mhagger/diff-slider-tools