exp, log, log1p

[riastradh-probcomp]

Proposal: In utils.py, rename

• careful_exp ---> exp
• extendedLog ---> log
• extendedLog1p ---> log1p

Import these unqualified and use them consistently, instead of math.* or numpy.*, wherever a single point is required. Continue to use numpy.* consistently where vectorization may be needed.

Rationale:

• The morphemes 'careful' and 'extended' convey little meaning here. ('Extended reals', as in \R + {\infty}? Not clear.)
• I still hate camel case.
• It is relatively unusual of IEEE 754 implementations that math.* raise exceptions on overflow by default, rather than returning infinities, and my impression is that I've encountered more bugs because of that than because of the converse. (This reason is subject to all sorts of cognitive biases.)
• numpy.* have considerable overhead vs math.* for the single-point case.
• If we ever change our minds about numpy overhead, we can just change the imports.

[axch]

Sounds good to me. This is an acceptable resolution to #534.

[riastradh-probcomp]

Whoops. I thought there was a related issue but overlooked #534 when I went looking for it a few minutes ago.

[riastradh-probcomp]

Addendum: Define expm1 in utils.py too.