Check tournament_size <= n_parents in hl_api

[HenrikMettler]

Makes the sanity check that the tournament size is smaller or equal to the number of parents in a population. Closes #246
Note that this PR is not ready for merging - due to the sanity checks various examples now raise errors. (Will adapt if the concept is approved)

[jakobj]

thanks for working on this!

however, i would strongly suggest to have such checks not only in the high level API, but deeper in the library. i think it makes most sense in mu_plus_lambda._create_offspring_population before doing anything else. there you have all information necessary to perform the check.

[coveralls]

Coverage decreased (-0.1%) to 94.957% when pulling 811df3e on HenrikMettler:enh/tournament_size into b6d7942 on Happy-Algorithms-League:master.

[HenrikMettler]

Note to myself: Address #271 within this PR

[HenrikMettler]

however, i would strongly suggest to have such checks not only in the high level API, but deeper in the library. i think it makes most sense in mu_plus_lambda._create_offspring_population before doing anything else. there you have all information necessary to perform the check.

I can move it there, but the downside is, that mu_plus_lambda._create_offspring_population is called within mu_plus_lambda.step -> the sanity check will be done at every time step which seems unreasonable to me.

[jakobj]

however, i would strongly suggest to have such checks not only in the high level API, but deeper in the library. i think it makes most sense in mu_plus_lambda._create_offspring_population before doing anything else. there you have all information necessary to perform the check.

I can move it there, but the downside is, that mu_plus_lambda._create_offspring_population is called within mu_plus_lambda.step -> the sanity check will be done at every time step which seems unreasonable to me.

indeed, the lower you go in the code the more often you will evaluate such checks. however, in terms of runtime we will not see any effect (+1 if per generation) while making the code more solid. so while in general i agree with your concern, in this case i think it's the best option.

[jakobj]

awesome, thanks! 👍

let's wait for travis to be happy before merging.