More precise mapping

[coatless]

Issue:

Mapping is done primarily using log(), logit(), or a customized range version.

In this case, we take a f:R->R^+

Idea:

Perhaps a better alternative is to use the hyperbolic tangent: tanh() that maps f:R -> [-1,1]

atanh(tanh(-2^4))
[1] -16.0003