Seep.jl

Because not everybody's data is big.

Basics: ANodes, Arrays, and Instances

Seep builds and evaluates computational flow graphs in julia. A computational flow graph (CFG) is a directed acyclic graph where nodes represent values and edges represent data dependencies. It is similar to the Single Static Assignment form of a program used by compilers, but there is no control flow. All nodes are evaluated each time the graph is executed.

The CFG is first defined as an abstract graph using ANodes. The abstract graph specifies the size and shape of each variable, how they are connected, and how each value will be computed. It does not allocate storage or define the order of operations.

One or more instances of may be constructed from the abstract graph. Each instance is a julia function that evaluates the CFG described by the abstract graph. Storage for the values of each ANode is allocated statically when the instance is constructed. In addition to being callable as a function, the instance provides access to the Arrays on which it operates.

Creating The Abstract Graph

Abstract graphs are built from ANodes. The first ANode defined is always an input ANode (the constructors of all of the other types require ANodes as arguments). Input ANodes are build by calling the ANode(name::String, dims::Int...) constructor. The name is optional, but it helps to make any code you will write using the instance a bit cleaner and sometimes also faster.

To get started, let's create an ANode to hold a single element, and call it x.

julia> x = ANode("x", 1)

Since it's often useful to create a ANode and assign it to a variable of the same name, there is a macro called @named to do exactly that. Let's create another ANode named y using the @named macro.

julia> @named y = ANode(1)

ANodes can be treated as if they were arrays in many cases. You can't index them (i.e. x[1] won't work) since they're abstract, but you can perform arithmetic on them. The result of operating on ANodes is always a new ANode that represents the computed value.

Let's create a couple more ANodes with compute simple functions of x and y.

julia> @named begin
  a = x + y
  b = 2a - log(y)
end

This creates 4 new ANodes: a, 2a, log(y), and b. Only a and b are named and assigned to variables in the workspace. 2a and log(y) are referenced by b, but not otherwise visible.

Instantiating the Graph

So far, we've created six ANodes. Let's instantiate the graph so we can use them.

julia> graph = instance(a, b)

Each ANode passed to the instance constructor will be evaluated exactly once when the instance is evaluated. All of the nodes they reference (e.g. 2a and log(y)) will also be evaluated as necessary.

Evaluating the Graph

To use the graph, we first have to provide values for the input nodes. The arrays that were allocated when the instance was created are available as fields of the instance. Let's populate the input ANodes' backing arrays with some data.

julia> graph.x[1] = 1
julia> graph.y[1] = 2

Now that the inputs are populated, we can evaluate the instance by calling it as a function.

julia> graph()

Finally, we can use the results by inspecting the arrays where the results are stored.

julia> println(graph.a)
julia> println(graph.b)

More Information

This has been a short introduction that shows only the most basic features of Seep. For mor information, see the doc/ directory in the root of the source tree.

• Supported Operations on ANodes
• Automatic Differentiation (and Gradient Descent)
• Memory Pools
• Convolution and Pooling

Disclaimer.

DISTRIBUTION STATEMENT A. Approved for public release: distribution unlimited.

© 2017 MASSACHUSETTS INSTITUTE OF TECHNOLOGY.

• Subject to FAR 52.227-11 – Patent Rights – Ownership by the Contractor (May 2014).
• SPDX-License-Identifier: MIT.

This material is based upon work supported by the Undersecretary of Defense for Research and Engineering under Air Force Contract No. FA8721-05-C-0002. Any opinions, findings, conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of USD(R&E).

The software/firmware is provided to you on an As-Is basis.