matsen/pplacer — Issue #211: replace `--unweighted` with a one-parameter transform
Author: matsen
Created: 2012-01-22 13:52:25+00:00
State: open
Labels: top

Analogous to the way the exponent works in `fpd`, I would like a `--kappa` flag defining an exponent that scales between a weighted and an unweighted version. The exponent will be named kappa. The end result will be a little different than what we were doing for unweighted, but oh well.

Given distal mass x, let y = x - (1-x). This is the usual transform specified in splitify.

Now, we would like to do a fractional exponentiation of y, but an issue is that values of x < 1/2 give negative values of y.

We just get around this by pulling out the sign:

sgn(y) |y|^kappa

Where sgn is just the sign function: http://en.wikipedia.org/wiki/Sgn

@cmccoy, could you please make an equivalent of `alpha_shape` for this function?

Stoked about this one.