greta-transforms: Transformation Functions for Greta Arrays
Description
transformations for greta arrays, which may also be
used as inverse link functions. Also see greta-operators and
greta-functions.
Usage
iprobit(x)
ilogit(x)
icloglog(x)
icauchit(x)
log1pe(x)
Arguments
x
a real-valued (i.e. values ranging from -Inf to Inf) greta array to
transform to a constrained value
Details
greta does not allow you to state the transformation/link on the
left hand side of an assignment, as is common in the BUGS and STAN
modelling languages. That's because the same syntax has a very different
meaning in R, and can only be applied to objects that are already in
existence. The inverse forms of the common link functions (prefixed with an
'i') are therefore more likely to useful in modelling, and these are what
are provided here.
The log1pe inverse link function is equivalent to log(1 + exp(x)),
yielding a positive transformed parameter. Unlike the log transformation,
this transformation is approximately linear for x > 1. i.e. when \(x >
1\), \(y \approx x\)
x = normal(1, 3, dim = 10)
# transformation to the unit interval p1 <- iprobit(x)
p2 <- ilogit(x)
p3 <- icloglog(x)
p4 <- icauchit(x)
# and to positive reals y <- log1pe(x)