Now that I actually tried to use it, I find the Harmonic class a bit
odd. For one thing the parameter is called "standard deviation" or
something, which doesn't mean anything for a harmonic. Secondly, once
you figure out what it is, it is multiplied by a many significant
figure constant before it is used (the documentation says this is for
modeller compatibility). This multiplier makes it very hard to use the
Harmonic as part of a scoring function (since it is hard to make the
composite function continuous).
Do we really want this? In my mind the thing that makes the most sense
is to to have a the mean and the spring constant be the parameters and
to get rid of the odd multiplier.