Numeric specifying concavity constant for implied step
weighting.
The most appropriate value will depend on the dataset, but values around
10--15 often perform well Goloboff2018,Smith2019TreeSearch.
The character string "profile" employs an approximation of profile parsimony
Faith2001TreeSearch.
Set as Inf
for equal step weights, which underperforms step weighting
approaches
Goloboff2008,Goloboff2018,Goloboff2019,Smith2019TreeSearch.