Really needs a docstring, practically more than anything else. 

The Trials class-level docstring is also pretty opaque and quite confusing to me: it seems to describe multiple "trial" documents, but you're instantiating a single "Trials" object and that's what the docstring is supposed to be describing, the container.

General comment: how many of these methods really need to be part of the _public_ interface of this class? It would help to make your intentions as to the public API clear by a) prefixing as many of them as possible with an underscore (stuff that never gets used outside of other methods in this class are good candidates) b) documenting the remaining ones at least as one-liners in the class docstring.

fmin would pretty clearly be something that remains part of the public API, though.