scikit-learn/scikit-learn — pull request #3365 by fabianp (2014-07-11 12:29:23+00:00)
Title: DOC: write cost function of logistic regression

Improve documentation of logistic regression by displaying the exact
form of the cost function (as is done for other models).

I feel it important to state clearly what is the cost function of the
model because:

* Some might want to compare their implementation against this one,
in which case it is important to know exactly what is the form of the
cost function.

* Furthermore since the models are quite inconsistent in terms of
notation for the regularization parameter: some models in this
module penalize by 1/C, others by alpha and others by alpha/2.