✨ 🔥 Implement backpropagation for NeuraGraph (untested)

src/algebra/mod.rs

@@ -1,4 +1,6 @@
 mod matrix;
+use std::any::Any;
+
 pub use matrix::NeuraMatrix;
 
 mod vector;
@@ -17,6 +19,39 @@ pub trait NeuraVectorSpace {
     fn norm_squared(&self) -> f64;
 }
 
+pub trait NeuraDynVectorSpace {
+    fn add_assign(&mut self, other: &dyn NeuraDynVectorSpace);
+
+    fn mul_assign(&mut self, by: f64);
+
+    fn norm_squared(&self) -> f64;
+
+    /// Trampoline for allowing NeuraDynVectorSpace to be cast back into a known type for add_assign
+    fn into_any(&self) -> &dyn Any;
+}
+
+impl<T: NeuraVectorSpace + 'static> NeuraDynVectorSpace for T {
+    fn add_assign(&mut self, other: &dyn NeuraDynVectorSpace) {
+        let Some(other) = other.into_any().downcast_ref::<Self>() else {
+            panic!("Incompatible operand: expected other to be equal to self");
+        };
+
+        <Self as NeuraVectorSpace>::add_assign(self, other);
+    }
+
+    fn mul_assign(&mut self, by: f64) {
+        <Self as NeuraVectorSpace>::mul_assign(self, by);
+    }
+
+    fn norm_squared(&self) -> f64 {
+        <Self as NeuraVectorSpace>::norm_squared(self)
+    }
+
+    fn into_any(&self) -> &dyn Any {
+        self
+    }
+}
+
 impl NeuraVectorSpace for () {
     #[inline(always)]
     fn add_assign(&mut self, _other: &Self) {

src/lib.rs

@@ -1,11 +1,11 @@
 pub mod algebra;
 pub mod derivable;
+pub mod err;
 pub mod gradient_solver;
 pub mod layer;
 pub mod network;
 pub mod train;
 
-pub mod err;
 mod utils;
 
 // TODO: move to a different file

src/network/graph/from.rs

@@ -2,60 +2,63 @@ use crate::network::residual::{NeuraAxisDefault, NeuraSplitInputs};
 
 use super::*;
 
-trait FromSequential<Seq, Data> {
-    fn from_sequential(
+pub trait FromSequential<Seq, Data> {
+    fn from_sequential_rec(
         seq: &Seq,
         nodes: Vec<NeuraGraphNodeConstructed<Data>>,
-        output_shape: NeuraShape,
+        input_shape: NeuraShape,
     ) -> Self;
 }
 
 impl<Data> FromSequential<(), Data> for NeuraGraph<Data> {
-    fn from_sequential(
+    fn from_sequential_rec(
         _seq: &(),
         nodes: Vec<NeuraGraphNodeConstructed<Data>>,
-        output_shape: NeuraShape,
+        input_shape: NeuraShape,
     ) -> Self {
         Self {
             output_index: nodes.len(),
             buffer_size: nodes.len() + 1,
             nodes: nodes,
-            output_shape,
+            output_shape: input_shape,
         }
     }
 }
 
-impl<
-        Data: Clone,
-        Layer: NeuraLayer<Data, Output = Data> + Clone + std::fmt::Debug + 'static,
-        ChildNetwork,
-    > FromSequential<NeuraSequential<Layer, ChildNetwork>, Data> for NeuraGraph<Data>
+impl<Data: Clone + 'static, Layer: NeuraTrainableLayerFull<Data, Output = Data>, ChildNetwork>
+    FromSequential<NeuraSequential<Layer, ChildNetwork>, Data> for NeuraGraph<Data>
 where
     NeuraGraph<Data>: FromSequential<ChildNetwork, Data>,
     NeuraAxisDefault: NeuraSplitInputs<Data, Combined = Data>,
+    Layer::IntermediaryRepr: 'static,
 {
-    fn from_sequential(
+    fn from_sequential_rec(
         seq: &NeuraSequential<Layer, ChildNetwork>,
         mut nodes: Vec<NeuraGraphNodeConstructed<Data>>,
-        output_shape: NeuraShape,
+        input_shape: NeuraShape,
     ) -> Self {
         nodes.push(NeuraGraphNodeConstructed {
-            node: Box::new(NeuraGraphNode::from(seq.layer.clone())),
+            node: Box::new(NeuraGraphNode::from_layer(
+                seq.layer.clone(),
+                vec![input_shape],
+            )),
             inputs: vec![nodes.len()],
             output: nodes.len() + 1,
         });
 
-        Self::from_sequential(&seq.child_network, nodes, output_shape)
+        Self::from_sequential_rec(&seq.child_network, nodes, seq.layer.output_shape())
     }
 }
 
-impl<Data, Layer, ChildNetwork> From<NeuraSequential<Layer, ChildNetwork>> for NeuraGraph<Data>
-where
-    NeuraGraph<Data>: FromSequential<NeuraSequential<Layer, ChildNetwork>, Data>,
-    NeuraSequential<Layer, ChildNetwork>: NeuraShapedLayer,
-{
-    fn from(network: NeuraSequential<Layer, ChildNetwork>) -> Self {
-        let output_shape = network.output_shape();
-        Self::from_sequential(&network, vec![], output_shape)
+impl<Data> NeuraGraph<Data> {
+    pub fn from_sequential<Layer, ChildNetwork>(
+        network: NeuraSequential<Layer, ChildNetwork>,
+        input_shape: NeuraShape,
+    ) -> Self
+    where
+        NeuraGraph<Data>: FromSequential<NeuraSequential<Layer, ChildNetwork>, Data>,
+        NeuraSequential<Layer, ChildNetwork>: NeuraShapedLayer,
+    {
+        Self::from_sequential_rec(&network, vec![], input_shape)
     }
 }

src/network/graph/mod.rs

@@ -1,4 +1,11 @@
-use crate::{layer::NeuraShapedLayer, prelude::*};
+use std::any::Any;
+
+use crate::{
+    algebra::NeuraDynVectorSpace,
+    derivable::NeuraLoss,
+    layer::{NeuraShapedLayer, NeuraTrainableLayerEval},
+    prelude::*,
+};
 
 mod node;
 pub use node::*;
@@ -7,9 +14,36 @@ mod partial;
 pub use partial::NeuraGraphPartial;
 
 mod from;
+pub use from::FromSequential;
+
+pub trait NeuraTrainableLayerFull<Input>:
+    NeuraTrainableLayerEval<Input>
+    + NeuraTrainableLayerBackprop<Input>
+    + NeuraTrainableLayerSelf<Input>
+    + NeuraShapedLayer
+    + Clone
+    + std::fmt::Debug
+    + 'static
+where
+    Self::IntermediaryRepr: 'static,
+{
+}
+
+impl<Input, T> NeuraTrainableLayerFull<Input> for T
+where
+    T: NeuraTrainableLayerEval<Input>
+        + NeuraTrainableLayerBackprop<Input>
+        + NeuraTrainableLayerSelf<Input>
+        + NeuraShapedLayer
+        + Clone
+        + std::fmt::Debug
+        + 'static,
+    T::IntermediaryRepr: 'static,
+{
+}
 
 #[derive(Debug)]
-struct NeuraGraphNodeConstructed<Data> {
+pub struct NeuraGraphNodeConstructed<Data> {
     node: Box<dyn NeuraGraphNodeEval<Data>>,
     inputs: Vec<usize>,
     output: usize,
@@ -48,10 +82,12 @@ impl<Data> NeuraGraph<Data> {
         res
     }
 
-    fn eval_in(&self, input: &Data, buffer: &mut Vec<Option<Data>>)
+    fn eval_in(&self, input: &Data, buffer: &mut [Option<Data>])
     where
         Data: Clone,
     {
+        assert!(buffer.len() >= self.nodes.len());
+
         buffer[0] = Some(input.clone());
 
         for node in self.nodes.iter() {
@@ -69,6 +105,77 @@ impl<Data> NeuraGraph<Data> {
             buffer[node.output] = Some(result);
         }
     }
+
+    fn backprop_in<Loss, Target>(
+        &self,
+        input: &Data,
+        loss: Loss,
+        target: &Target,
+        output_buffer: &mut Vec<Option<Data>>,
+        backprop_buffer: &mut Vec<Option<Data>>,
+        intermediary_buffer: &mut Vec<Option<Box<dyn Any>>>,
+        gradient_buffer: &mut Vec<Box<dyn NeuraDynVectorSpace>>,
+    ) where
+        Data: Clone + std::ops::Add<Data, Output = Data>,
+        Loss: NeuraLoss<Data, Target = Target>,
+    {
+        assert!(output_buffer.len() >= self.nodes.len());
+        assert!(backprop_buffer.len() >= self.nodes.len());
+        assert!(intermediary_buffer.len() >= self.nodes.len());
+        assert!(gradient_buffer.len() >= self.nodes.len());
+
+        output_buffer[0] = Some(input.clone());
+
+        // Forward pass
+        for node in self.nodes.iter() {
+            // PERF: re-use the allocation for `inputs`, and `.take()` the elements only needed once?
+            let inputs: Vec<_> = node
+                .inputs
+                .iter()
+                .map(|&i| {
+                    output_buffer[i]
+                        .clone()
+                        .expect("Unreachable: output of previous layer was not set")
+                })
+                .collect();
+            let (result, intermediary) = node.node.eval_training(&inputs);
+
+            output_buffer[node.output] = Some(result);
+            intermediary_buffer[node.output] = Some(intermediary);
+        }
+
+        let loss = loss.nabla(
+            target,
+            output_buffer[self.output_index]
+                .as_ref()
+                .expect("Unreachable: output was not set"),
+        );
+        backprop_buffer[self.output_index] = Some(loss);
+
+        // Backward pass
+        for node in self.nodes.iter().rev() {
+            let Some(epsilon_in) = backprop_buffer[node.output].take() else {
+                continue
+            };
+
+            let epsilon_out = node
+                .node
+                .backprop(&intermediary_buffer[node.output], &epsilon_in);
+            let gradient = node
+                .node
+                .get_gradient(&intermediary_buffer[node.output], &epsilon_in);
+
+            gradient_buffer[node.output].add_assign(&*gradient);
+
+            for (&input, epsilon) in node.inputs.iter().zip(epsilon_out.into_iter()) {
+                if let Some(existing_gradient) = backprop_buffer[input].take() {
+                    backprop_buffer[input] = Some(existing_gradient + epsilon);
+                } else {
+                    backprop_buffer[input] = Some(epsilon);
+                }
+            }
+        }
+    }
 }
 
 impl<Data: Clone> NeuraLayer<Data> for NeuraGraph<Data> {
@@ -213,7 +320,7 @@ mod test {
         .construct(NeuraShape::Vector(3))
         .unwrap();
 
-        let graph = NeuraGraph::from(network.clone());
+        let graph = NeuraGraph::from_sequential(network.clone(), NeuraShape::Vector(3));
 
         for _ in 0..10 {
             let input = uniform_vector(3);

src/network/graph/node.rs

@@ -1,13 +1,16 @@
 use dyn_clone::DynClone;
-use std::fmt::Debug;
+use std::{any::Any, fmt::Debug};
 
 use crate::{
+    algebra::NeuraDynVectorSpace,
     err::NeuraAxisErr,
-    layer::{NeuraLayer, NeuraShapedLayer},
+    layer::{NeuraShapedLayer, NeuraTrainableLayerEval},
     network::residual::{NeuraAxisDefault, NeuraCombineInputs, NeuraSplitInputs},
     prelude::{NeuraPartialLayer, NeuraShape},
 };
 
+use super::*;
+
 // TODO: split into two  traits
 pub trait NeuraGraphNodePartial<Data>: DynClone + Debug {
     fn inputs<'a>(&'a self) -> &'a [String];
@@ -20,7 +23,17 @@ pub trait NeuraGraphNodePartial<Data>: DynClone + Debug {
 }
 
 pub trait NeuraGraphNodeEval<Data>: DynClone + Debug {
-    fn eval<'a>(&'a self, inputs: &[Data]) -> Data;
+    fn eval(&self, inputs: &[Data]) -> Data;
+
+    fn eval_training(&self, inputs: &[Data]) -> (Data, Box<dyn Any>);
+    fn backprop(&self, intermediary: &dyn Any, epsilon_in: &Data) -> Vec<Data>;
+    fn get_gradient(
+        &self,
+        intermediary: &dyn Any,
+        epsilon_in: &Data,
+    ) -> Box<dyn NeuraDynVectorSpace>;
+
+    fn apply_gradient(&mut self, gradient: &dyn NeuraDynVectorSpace);
 }
 
 #[derive(Clone, Debug)]
@@ -29,6 +42,21 @@ pub struct NeuraGraphNode<Axis, Layer> {
     axis: Axis,
     layer: Layer,
     name: String,
+
+    input_shapes: Option<Vec<NeuraShape>>,
+}
+
+impl<Layer> NeuraGraphNode<NeuraAxisDefault, Layer> {
+    pub(crate) fn from_layer(layer: Layer, input_shapes: Vec<NeuraShape>) -> Self {
+        Self {
+            inputs: vec![],
+            axis: NeuraAxisDefault,
+            layer,
+            name: random_name(),
+
+            input_shapes: Some(input_shapes),
+        }
+    }
 }
 
 impl<Axis, Layer> NeuraGraphNode<Axis, Layer> {
@@ -39,6 +67,8 @@ impl<Axis, Layer> NeuraGraphNode<Axis, Layer> {
             axis,
             layer,
             name,
+
+            input_shapes: None,
         }
     }
 
@@ -50,38 +80,101 @@ impl<Axis, Layer> NeuraGraphNode<Axis, Layer> {
             + Debug
             + 'static,
         Layer: NeuraPartialLayer + Clone + Debug + 'static,
-        Layer::Constructed: NeuraShapedLayer
-            + NeuraLayer<<Axis as NeuraCombineInputs<Data>>::Combined, Output = Data>
-            + Clone
-            + Debug
-            + 'static,
+        Layer::Constructed:
+            NeuraTrainableLayerFull<<Axis as NeuraCombineInputs<Data>>::Combined, Output = Data>,
         Layer::Err: Debug,
+        <Layer::Constructed as NeuraTrainableLayerEval<
+            <Axis as NeuraCombineInputs<Data>>::Combined,
+        >>::IntermediaryRepr: 'static,
+        <Axis as NeuraCombineInputs<Data>>::Combined: 'static,
     {
         Box::new(self)
     }
+
+    fn downcast_intermediary<'a, Data>(
+        &self,
+        intermediary: &'a dyn Any,
+    ) -> &'a Intermediary<Axis::Combined, Layer>
+    where
+        Axis: NeuraCombineInputs<Data>,
+        Layer: NeuraTrainableLayerFull<Axis::Combined>,
+        Axis::Combined: 'static,
+    {
+        intermediary
+            .downcast_ref::<Intermediary<Axis::Combined, Layer>>()
+            .expect("Incompatible value passed to NeuraGraphNode::backprop")
+    }
+}
+
+struct Intermediary<Combined, Layer: NeuraTrainableLayerFull<Combined>>
+where
+    Layer::IntermediaryRepr: 'static,
+{
+    combined: Combined,
+    layer_intermediary: Layer::IntermediaryRepr,
 }
 
 impl<
         Data: Clone,
         Axis: NeuraSplitInputs<Data> + Clone + Debug,
-        Layer: NeuraLayer<<Axis as NeuraCombineInputs<Data>>::Combined, Output = Data> + Clone + Debug,
+        Layer: NeuraTrainableLayerFull<<Axis as NeuraCombineInputs<Data>>::Combined, Output = Data>,
     > NeuraGraphNodeEval<Data> for NeuraGraphNode<Axis, Layer>
+where
+    Layer::IntermediaryRepr: 'static,
+    Axis::Combined: 'static,
 {
     fn eval<'a>(&'a self, inputs: &[Data]) -> Data {
         // TODO: use to_vec_in?
         let combined = self.axis.combine(inputs.to_vec());
         self.layer.eval(&combined)
     }
-}
 
-impl<Layer: Clone + Debug> From<Layer> for NeuraGraphNode<NeuraAxisDefault, Layer> {
-    fn from(layer: Layer) -> Self {
-        Self {
-            inputs: vec![],
-            axis: NeuraAxisDefault,
-            layer,
-            name: random_name(),
-        }
+    fn eval_training<'a>(&self, inputs: &[Data]) -> (Data, Box<dyn Any>) {
+        let combined = self.axis.combine(inputs.to_vec());
+        let (result, layer_intermediary) = self.layer.eval_training(&combined);
+
+        let intermediary: Intermediary<Axis::Combined, Layer> = Intermediary {
+            combined,
+            layer_intermediary,
+        };
+
+        (result, Box::new(intermediary))
+    }
+
+    fn backprop(&self, intermediary: &dyn Any, epsilon_in: &Data) -> Vec<Data> {
+        let intermediary = self.downcast_intermediary(intermediary);
+
+        let epsilon_out = self.layer.backprop_layer(
+            &intermediary.combined,
+            &intermediary.layer_intermediary,
+            epsilon_in,
+        );
+
+        self.axis
+            .split(&epsilon_out, self.input_shapes.as_ref().unwrap())
+    }
+
+    fn get_gradient(
+        &self,
+        intermediary: &dyn Any,
+        epsilon_in: &Data,
+    ) -> Box<dyn NeuraDynVectorSpace> {
+        let intermediary = self.downcast_intermediary(intermediary);
+
+        Box::new(self.layer.get_gradient(
+            &intermediary.combined,
+            &intermediary.layer_intermediary,
+            epsilon_in,
+        ))
+    }
+
+    fn apply_gradient(&mut self, gradient: &dyn NeuraDynVectorSpace) {
+        self.layer.apply_gradient(
+            gradient
+                .into_any()
+                .downcast_ref::<Layer::Gradient>()
+                .expect("Invalid gradient type passed to NeuraGraphNode::apply_gradient"),
+        );
     }
 }
 
@@ -95,12 +188,10 @@ impl<
         Layer: NeuraPartialLayer + Clone + Debug,
     > NeuraGraphNodePartial<Data> for NeuraGraphNode<Axis, Layer>
 where
-    Layer::Constructed: NeuraShapedLayer
-        + NeuraLayer<<Axis as NeuraCombineInputs<Data>>::Combined, Output = Data>
-        + Clone
-        + Debug
-        + 'static,
+    Layer::Constructed: NeuraTrainableLayerFull<<Axis as NeuraCombineInputs<Data>>::Combined, Output = Data>,
     Layer::Err: Debug,
+    <Layer::Constructed as NeuraTrainableLayerEval<<Axis as NeuraCombineInputs<Data>>::Combined>>::IntermediaryRepr: 'static,
+    <Axis as NeuraCombineInputs<Data>>::Combined: 'static,
 {
     fn inputs<'a>(&'a self) -> &'a [String] {
         &self.inputs
@@ -116,7 +207,7 @@ where
     ) -> Result<(Box<dyn NeuraGraphNodeEval<Data>>, NeuraShape), String> {
         let combined = self
             .axis
-            .combine(input_shapes)
+            .combine(input_shapes.clone())
             .map_err(|err| format!("{:?}", err))?;
 
         let constructed_layer = self
@@ -132,6 +223,7 @@ where
                 axis: self.axis.clone(),
                 layer: constructed_layer,
                 name: self.name.clone(),
+                input_shapes: Some(input_shapes)
             }),
             output_shape,
         ))