feat(spiel_bot): network with mlp and resnet

spiel_bot/src/network/mlp.rs

@@ -0,0 +1,223 @@
+//! Two-hidden-layer MLP policy-value network.
+//!
+//! ```text
+//! Input [B, obs_size]
+//!   → Linear(obs → hidden) → ReLU
+//!   → Linear(hidden → hidden) → ReLU
+//!   ├─ policy_head: Linear(hidden → action_size)  [raw logits]
+//!   └─ value_head:  Linear(hidden → 1) → tanh     [∈ (-1, 1)]
+//! ```
+
+use burn::{
+    module::Module,
+    nn::{Linear, LinearConfig},
+    record::{CompactRecorder, Recorder},
+    tensor::{
+        activation::{relu, tanh},
+        backend::Backend,
+        Tensor,
+    },
+};
+use std::path::Path;
+
+use super::PolicyValueNet;
+
+// ── Config ────────────────────────────────────────────────────────────────────
+
+/// Configuration for [`MlpNet`].
+#[derive(Debug, Clone)]
+pub struct MlpConfig {
+    /// Number of input features.  217 for Trictrac's `to_tensor()`.
+    pub obs_size: usize,
+    /// Number of output actions.  514 for Trictrac's `ACTION_SPACE_SIZE`.
+    pub action_size: usize,
+    /// Width of both hidden layers.
+    pub hidden_size: usize,
+}
+
+impl Default for MlpConfig {
+    fn default() -> Self {
+        Self {
+            obs_size: 217,
+            action_size: 514,
+            hidden_size: 256,
+        }
+    }
+}
+
+// ── Network ───────────────────────────────────────────────────────────────────
+
+/// Simple two-hidden-layer MLP with shared trunk and two heads.
+///
+/// Prefer this over [`ResNet`](super::ResNet) when training time is a
+/// priority, or as a fast baseline.
+#[derive(Module, Debug)]
+pub struct MlpNet<B: Backend> {
+    fc1: Linear<B>,
+    fc2: Linear<B>,
+    policy_head: Linear<B>,
+    value_head: Linear<B>,
+}
+
+impl<B: Backend> MlpNet<B> {
+    /// Construct a fresh network with random weights.
+    pub fn new(config: &MlpConfig, device: &B::Device) -> Self {
+        Self {
+            fc1: LinearConfig::new(config.obs_size, config.hidden_size).init(device),
+            fc2: LinearConfig::new(config.hidden_size, config.hidden_size).init(device),
+            policy_head: LinearConfig::new(config.hidden_size, config.action_size).init(device),
+            value_head: LinearConfig::new(config.hidden_size, 1).init(device),
+        }
+    }
+
+    /// Save weights to `path` (MessagePack format via [`CompactRecorder`]).
+    ///
+    /// The file is written exactly at `path`; callers should append `.mpk` if
+    /// they want the conventional extension.
+    pub fn save(&self, path: &Path) -> anyhow::Result<()> {
+        CompactRecorder::new()
+            .record(self.clone().into_record(), path.to_path_buf())
+            .map_err(|e| anyhow::anyhow!("MlpNet::save failed: {e:?}"))
+    }
+
+    /// Load weights from `path` into a fresh model built from `config`.
+    pub fn load(config: &MlpConfig, path: &Path, device: &B::Device) -> anyhow::Result<Self> {
+        let record = CompactRecorder::new()
+            .load(path.to_path_buf(), device)
+            .map_err(|e| anyhow::anyhow!("MlpNet::load failed: {e:?}"))?;
+        Ok(Self::new(config, device).load_record(record))
+    }
+}
+
+impl<B: Backend> PolicyValueNet<B> for MlpNet<B> {
+    fn forward(&self, obs: Tensor<B, 2>) -> (Tensor<B, 2>, Tensor<B, 2>) {
+        let x = relu(self.fc1.forward(obs));
+        let x = relu(self.fc2.forward(x));
+        let policy = self.policy_head.forward(x.clone());
+        let value = tanh(self.value_head.forward(x));
+        (policy, value)
+    }
+}
+
+// ── Tests ─────────────────────────────────────────────────────────────────────
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use burn::backend::NdArray;
+
+    type B = NdArray<f32>;
+
+    fn device() -> <B as Backend>::Device {
+        Default::default()
+    }
+
+    fn default_net() -> MlpNet<B> {
+        MlpNet::new(&MlpConfig::default(), &device())
+    }
+
+    fn zeros_obs(batch: usize) -> Tensor<B, 2> {
+        Tensor::zeros([batch, 217], &device())
+    }
+
+    // ── Shape tests ───────────────────────────────────────────────────────
+
+    #[test]
+    fn forward_output_shapes() {
+        let net = default_net();
+        let obs = zeros_obs(4);
+        let (policy, value) = net.forward(obs);
+
+        assert_eq!(policy.dims(), [4, 514], "policy shape mismatch");
+        assert_eq!(value.dims(), [4, 1], "value shape mismatch");
+    }
+
+    #[test]
+    fn forward_single_sample() {
+        let net = default_net();
+        let (policy, value) = net.forward(zeros_obs(1));
+        assert_eq!(policy.dims(), [1, 514]);
+        assert_eq!(value.dims(), [1, 1]);
+    }
+
+    // ── Value bounds ──────────────────────────────────────────────────────
+
+    #[test]
+    fn value_in_tanh_range() {
+        let net = default_net();
+        // Use a non-zero input so the output is not trivially at 0.
+        let obs = Tensor::<B, 2>::ones([8, 217], &device());
+        let (_, value) = net.forward(obs);
+        let data: Vec<f32> = value.into_data().to_vec().unwrap();
+        for v in &data {
+            assert!(
+                *v > -1.0 && *v < 1.0,
+                "value {v} is outside open interval (-1, 1)"
+            );
+        }
+    }
+
+    // ── Policy logits ─────────────────────────────────────────────────────
+
+    #[test]
+    fn policy_logits_not_all_equal() {
+        // With random weights the 514 logits should not all be identical.
+        let net = default_net();
+        let (policy, _) = net.forward(zeros_obs(1));
+        let data: Vec<f32> = policy.into_data().to_vec().unwrap();
+        let first = data[0];
+        let all_same = data.iter().all(|&x| (x - first).abs() < 1e-6);
+        assert!(!all_same, "all policy logits are identical — network may be degenerate");
+    }
+
+    // ── Config propagation ────────────────────────────────────────────────
+
+    #[test]
+    fn custom_config_shapes() {
+        let config = MlpConfig {
+            obs_size: 10,
+            action_size: 20,
+            hidden_size: 32,
+        };
+        let net = MlpNet::<B>::new(&config, &device());
+        let obs = Tensor::zeros([3, 10], &device());
+        let (policy, value) = net.forward(obs);
+        assert_eq!(policy.dims(), [3, 20]);
+        assert_eq!(value.dims(), [3, 1]);
+    }
+
+    // ── Save / Load ───────────────────────────────────────────────────────
+
+    #[test]
+    fn save_load_preserves_weights() {
+        let config = MlpConfig::default();
+        let net = default_net();
+
+        // Forward pass before saving.
+        let obs = Tensor::<B, 2>::ones([2, 217], &device());
+        let (policy_before, value_before) = net.forward(obs.clone());
+
+        // Save to a temp file.
+        let path = std::env::temp_dir().join("spiel_bot_test_mlp.mpk");
+        net.save(&path).expect("save failed");
+
+        // Load into a fresh model.
+        let loaded = MlpNet::<B>::load(&config, &path, &device()).expect("load failed");
+        let (policy_after, value_after) = loaded.forward(obs);
+
+        // Outputs must be bitwise identical.
+        let p_before: Vec<f32> = policy_before.into_data().to_vec().unwrap();
+        let p_after: Vec<f32> = policy_after.into_data().to_vec().unwrap();
+        for (i, (a, b)) in p_before.iter().zip(p_after.iter()).enumerate() {
+            assert!((a - b).abs() < 1e-3, "policy[{i}]: {a} vs {b} differ by more than tolerance");
+        }
+
+        let v_before: Vec<f32> = value_before.into_data().to_vec().unwrap();
+        let v_after: Vec<f32> = value_after.into_data().to_vec().unwrap();
+        for (i, (a, b)) in v_before.iter().zip(v_after.iter()).enumerate() {
+            assert!((a - b).abs() < 1e-3, "value[{i}]: {a} vs {b} differ by more than tolerance");
+        }
+
+        let _ = std::fs::remove_file(path);
+    }
+}