Description Usage Arguments Details See Also
Some useful parameter transformations.
1 2 3 4 5 6 7 | logit(p)
expit(x)
log_barycentric(X)
inv_log_barycentric(Y)
|
p |
numeric; a quantity in [0,1]. |
x |
numeric; the log odds ratio. |
X |
numeric; a vector containing the quantities to be transformed according to the log-barycentric transformation. |
Y |
numeric; a vector containing the log fractions. |
Parameter transformations can be used in many cases to recast constrained optimization problems as unconstrained problems.
Although there are no limits to the transformations one can implement using the parameter_trans
facilty, pomp provides a few ready-built functions to implement some very commonly useful ones.
The logit transformation takes a probability p to its log odds, log(p/(1-p)). It maps the unit interval [0,1] into the extended real line [-∞,∞].
The inverse of the logit transformation is the expit transformation.
The log-barycentric transformation takes a vector Xi, i=1,…,n, to a vector Yi, where
Yi = log(Xi/sum(Xi)).
If X is an n-vector, it takes every simplex defined by sum(Xi)=c, c constant, to n-dimensional Euclidean space R^n.
The inverse of the log-barycentric transformation is implemented as inv_log_barycentric
.
Note that it is not a true inverse, in the sense that it takes R^n to the unit simplex, sum(Xi)=1.
Thus,
1 | log_barycentric(inv_log_barycentric(Y)) == Y,
|
but
1 | inv_log_barycentric(log_barycentric(X)) == X
|
only if sum(X) == 1
.
Other information on model implementation: Csnippet
,
accumulators
,
covariate_table
,
distributions
, dmeasure_spec
,
dprocess_spec
,
parameter_trans
,
pomp2-package
, prior_spec
,
rinit_spec
, rmeasure_spec
,
rprocess_spec
, skeleton_spec
,
userdata
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.