Potential m3n issue

[Namita Gupta]

histogram for distToNearest with m3n has a significantly tinier second mode than any of the other four methods. Possible bug in targeting model, may need a double-check.

[Jason Vander Heiden]

The 3-mer mutability is missing values (ie they are mutability = 0 in the Smith et al, 1996 paper), which appears to be the source of zeros and extra NAs in the targeting model. Also, the mutability values in data-raw/M3N_Mutability.csv don't match those in the Smith et al, 1996 paper.

This might not be the only problem, but it is a problem... I think we need to impute the missing data.

[Jason Vander Heiden]

We removed the M3N model entirely.