Add MHAAddNorm

src/nn/attention.rs

@@ -12,21 +12,18 @@ pub struct MultiHeadAttention {
     key_proj: Linear,
     query_proj: Linear,
     value_proj: Linear,
-
-    dense: Linear,
-    norm: Normalization,
     // TODO: dropout
 }
 
 impl MultiHeadAttention {
     pub fn new(
         embed_dim: usize,
         num_heads: usize,
-        layer_norm_eps: f32,
         w: impl Initializer<ParamNDA> + Scope,
         b: impl Initializer<ParamNDA> + Scope,
-        opt: impl Optimizer<NDArray> + Clone,
     ) -> Self {
+        assert!(embed_dim % num_heads == 0);
+
         MultiHeadAttention {
             head_dim: embed_dim / num_heads,
             num_heads,
@@ -48,13 +45,6 @@ impl MultiHeadAttention {
                 w.scope("value_proj"),
                 Some(b.scope("value_proj")),
             ),
-            dense: Linear::new(
-                embed_dim,
-                embed_dim,
-                w.scope("dense"),
-                Some(b.scope("dense")),
-            ),
-            norm: Normalization::new(vec![1], layer_norm_eps, opt),
         }
     }
 
@@ -82,10 +72,9 @@ impl MultiHeadAttention {
         let attention_value = attention.matmul(&value);
 
         // (N, num_heads, L, head_dim) -> (N, L, num_heads * head_dim)
-        let attention_value = self.merge_heads(attention_value);
+        let y = self.merge_heads(attention_value);
 
-        let y = self.dense.call(attention_value, train);
-        self.norm.call(&y + x, train)
+        y
     }
 
     fn separate_heads(&self, features: ComputedNDA) -> ComputedNDA {
@@ -124,6 +113,35 @@ impl MultiHeadAttention {
     }
 }
 
+pub struct MHAAddNorm {
+    attention: MultiHeadAttention,
+    dense: Linear,
+    norm: Normalization,
+}
+
+impl MHAAddNorm {
+    pub fn new(
+        dim: usize,
+        num_heads: usize,
+        layer_norm_eps: f32,
+        w: impl Initializer<ParamNDA> + Scope,
+        b: impl Initializer<ParamNDA> + Scope,
+        opt: impl Optimizer<NDArray> + Clone,
+    ) -> Self {
+        Self {
+            attention: MultiHeadAttention::new(dim, num_heads, w.scope("mha"), b.scope("mha")),
+            dense: Linear::new(dim, dim, w.scope("dense"), Some(b.scope("dense"))),
+            norm: Normalization::new(vec![1], layer_norm_eps, opt),
+        }
+    }
+
+    pub fn call(&self, x: &ComputedNDA, attn_mask: &ComputedNDA, train: bool) -> ComputedNDA {
+        let y = self.attention.call(x, attn_mask, train);
+        let y = self.dense.call(y, train);
+        self.norm.call(&y + x, train)
+    }
+}
+
 #[test]
 fn test() {
     use ndarray_rand::rand_distr::Uniform;
@@ -133,7 +151,7 @@ fn test() {
         optimizers::Adam::new(),
     );
 
-    let mha = MultiHeadAttention::new(
+    let mha = MHAAddNorm::new(
         64,
         4,
         1e-5,