Vertices

There are several families of vertices. Each family shares a common value type.

Probabilistic

Probabilistic vertices are vertices that do not depend completely on their parent vertices. An example of this is a GaussianVertex which is non-deterministic and has a probability distribution controlled by parameters that come from its parents.

Changing the value of their parent vertices may change the probability density function but it will not directly cause a change of the value of the vertex.

Non-Probabilistic

The value of these vertices are completely dependent on their parent vertices’ values. For example, given C = A * B (for any vertices A and B), C is a non-probabilistic vertex. Even if A or B are probabilistic vertices, C is still completely dependent on their values which means it is non-probabilistic.

The Double Family

A DoubleVertex can be used by most arithmetic operators. They can be used to describe a problem that can be solved using gradient ascent optimization and their value is a double.

The currently available double vertices are

The Integer Family

An IntegerVertex is similar to the DoubleVertex except its value is an integer.

The currently available integer vertices are

The Boolean (true/false) Family

A BoolVertex can be used by most boolean operators. These can be observed directly and used in MCMC.

The currently available boolean vertices are

The Generic (everything else) family

These are the vertices that can have any type as a value. For example, this type can be an Enum or any user defined object. Let’s look at an example of this in Keanu with the CategoricalVertex which will return a value of the specified Enum MyType.

public enum MyType {
    A, B, C, D
}

public CategoricalVertex<MyType> getSelectorForMyType() {

    LinkedHashMap<MyType, DoubleVertex> frequency = new LinkedHashMap<>();
    frequency.put(A, new ConstantDoubleVertex(0.25));
    frequency.put(B, new ConstantDoubleVertex(0.25));
    frequency.put(C, new ConstantDoubleVertex(0.25));
    frequency.put(D, new ConstantDoubleVertex(0.25));

    return new CategoricalVertex<>(frequency);
}

The getSelectorForMyType() method returns a probabilistic vertex that would contain an object of type MyType A, B, C or D, 25% of the time respectively.

The currently available generic vertices are

Tensors

Vertices also have a shape, which describes the tensor shape contained within them. A vertex with shape [2,2] represents a 2 by 2 matrix. A vertex of shape [1,3] represents a row vector of length 3. The shape can have any number of dimensions and any length.