Math behind eval_count_of_generated_ft() in VW

In this post I would like to explain math used in eval_count_of_generated_ft() function proposed as a part of new interactions generation mechanism to VW 7.10.1 master branch.

Fixing 'best constant' and 'best constant loss' in VW

It's well-known that best constant value that printed by VW in work summary is correct only for squared loss. I have also pointed out that best constant loss value is never printed out for classes other than {0,1} and John Langford suggested anyone to try to fix this or he may remove it at all otherwise.

So, I have decided to try. Below is quite scrupulous description of what and why have I done in code so anyone could easily verify my conclusions. I nigher ML nor mapple expert so such verification really has sense.

Debugging VW with QtCreator on Linux

While playing with Vowpal Wabbit I have struggled many times with impossibility to debug VW sources in IDE and check how exactly it works. As I've recently finally switched to Kubuntu I don't want to launch Win every time I'm facing small problems. And unfortunately VWs sources equipped with Visual Studio project files which doesn't support *nix platforms.

Finally I've forced myself to try building VW on Linux as Qt project with QtCeator IDE. Surprisingly it was very easy to do in just a few steps: