Gorgonia as a clean backend

[owulveryck]

For the POC, Gorgonia has been heavily tweaked to fit the gonum's GraphBuilder interface.

The tweaked version has been vendored as an example. This leads to a maintenance problem.
It's merely impossible to add new features to the backend.

The Gorgonia team is working on a significant refactor of the API.
Meanwhile, I am considering rewriting the Gorgonia backend to use the actual API.

My idea is to use something similar to what I did with gorgonnx some time ago.

We can create a simple GorgoniaGraph in the backend fulfilling the interfaces:

• gonum.WeightedGraphBuilder
• OperationCarrier
• and issuing nodes compatible with TensorCarrier

and then a method

func (g *GorgoniaGraph) ToExprGraph() (*gorgonia.ExprGraph, error)

That would turn the graph into a gorgonia exprgraph by walking the graph starting from the input and creating the node accordingly.

Example. Assume an equation y = a * x + b that would produce this graph:

y -> add
add -> mul
add -> b
mul -> a
mul -> x

properly encoded into a Weighted Graph.

The ToExprGraph would then walk the graph (still have to figure out how to efficiently walk the graph) and create:

a := gorgonia.NodeFromAny(aT) // aT is already a tensor.Tensor
x := gorgonia.NodeFromAny(xT) // ...
// ...
m := gorgonia.Must(gorgonia.Mul(a,x))
add := gorgonia.Must(gorgonia.Add(m. b)

Do you get the drill?

What do you think?

[owulveryck]

Branch gorgonia is a work in progress to make Gorgonia compatible with the backend.ComputationGraph interface

[owulveryck]

In progress:

cd $GOPATH/src/github.com/owulveryck/onnx-go/backend/x/gorgonnx

go test -v
=== RUN   TestAbs
=== RUN   TestAbs/TestAbs
--- PASS: TestAbs (0.00s)
    --- PASS: TestAbs/TestAbs (0.00s)
=== RUN   TestAdd
=== RUN   TestAdd/TestAdd
=== RUN   TestAdd/TestAddBcast
--- FAIL: TestAdd (0.00s)
    --- PASS: TestAdd/TestAdd (0.00s)
    --- FAIL: TestAdd/TestAddBcast (0.00s)
        test_structure.go:84: Failed to infer shape. Op: + false: Shape mismatch: (3, 4, 5) and (5)
=== RUN   TestCos
=== RUN   TestCos/TestCos
=== RUN   TestCos/TestCosExample
--- PASS: TestCos (0.00s)
    --- PASS: TestCos/TestCos (0.00s)
    --- PASS: TestCos/TestCosExample (0.00s)
FAIL
exit status 1
FAIL    github.com/owulveryck/onnx-go/backend/x/gorgonnx        0.034s

Obviously, the broadcast does not work out-of-the-box, but I will work on it.

Next:

• implement an operation with attributes (convolution is a good choice)
• refactor the existing code
• create a skeleton and the associated doc to easily add new operators