Plate

class alan.Plate(**kwargs)[source]

The key class used to define your model: all random variables, are defined within a Plate.

An example plate definition:

Plate(
    a = Normal(0., 1.),
    g = Group(
        b = Normal('a', 1.),
        c = Normal('b', 1.),
    ),
    p = Plate(
        d = Data(),
    ),
)

Everything in the plate is specified as a keyword argument (i.e. of the form name = thing), where thing could be:

a distribution (see Distributions).
a Group.
a sub-plate Plate.
Data().

Critically, the name becomes the name of that thing. So in the above example, we have normal random variables named a, b, and c, a group named g, a sub-plate named p, and a random variable that will be associated with data, (see Data).

Note

In standard Bayesian terminology, including a variable within a plate indicates that there is actually several of these variables. That’s precisely how we’re using sub-plates: each subplates (p in the example) with have an assigned platesize, and we’ll replicate each variable within the plate that number of times.

Note that we also use Plate at the top-layer, even though we only have one copy of the top-layer variables.