Initialize using the trimmed mean of the trait.
initPositionParameter(trait)
The initial position parameter.
named vector of traits at the tips.
Rothenberg T. J., Fisher F. M., Tilanus C. B. 1964. A Note on Estimation from a Cauchy Sample. Journal of the American Statistical Association. 59:460–463. Rousseeuw P.J., Croux C. 1993. Alternatives to the Median Absolute Deviation. Journal of the American Statistical Association. 88:1273–1283.