cleanup jax

labml_nn/transformers/jax_transformer/__init__.py

@@ -422,43 +422,6 @@ class LayerNorm(Module):
         return x_norm
 
 
-class PrepareForMultiHeadAttention(Module):
-    """
-    <a id="PrepareMHA"></a>
-
-    ## Prepare for multi-head attention
-
-    This module does a linear transformation and splits the vector into given
-    number of heads for multi-head attention.
-    This is used to transform **key**, **query**, and **value** vectors.
-    """
-
-    def __init__(self, rnd_key: jax.random.PRNGKey, d_model: int, heads: int, d_k: int):
-        super().__init__()
-        # Linear layer for linear transform
-        self.linear = Linear(rnd_key, d_model, heads * d_k)
-        # Number of heads
-        self.heads = heads
-        # Number of dimensions in vectors in each head
-        self.d_k = d_k
-
-    def __call__(self, x: jnp.ndarray):
-        # Input has shape `[seq_len, batch_size, d_model]` or `[batch_size, d_model]`.
-        # We apply the linear transformation to the last dimension and split that into
-        # the heads.
-        head_shape = x.shape[:-1]
-
-        # Linear transform
-        x = self.linear(x)
-
-        # Split last dimension into heads
-
-        x = x.reshape(*head_shape, self.heads, self.d_k)
-
-        # Output has shape `[seq_len, batch_size, heads, d_k]` or `[batch_size, d_model]`
-        return x
-
-
 class MultiHeadAttention(Module):
     r"""
     <a id="MHA"></a>
@@ -503,9 +466,9 @@ class MultiHeadAttention(Module):
         self.heads = heads
 
         # These transform the `query`, `key` and `value` vectors for multi-headed attention.
-        self.query = PrepareForMultiHeadAttention(rnd_keys[0], d_model, heads, self.d_k)
-        self.key = PrepareForMultiHeadAttention(rnd_keys[1], d_model, heads, self.d_k)
-        self.value = PrepareForMultiHeadAttention(rnd_keys[2], d_model, heads, self.d_k)
+        self.query = Linear(rnd_keys[0], d_model, d_model)
+        self.key = Linear(rnd_keys[1], d_model, d_model)
+        self.value = Linear(rnd_keys[2], d_model, d_model)
 
         # Output layer
         self.output = Linear(rnd_keys[3], d_model, d_model)
@@ -537,12 +500,18 @@ class MultiHeadAttention(Module):
             # Same mask applied to all heads.
             mask = mask[:, :, None]
 
-        # Prepare `query`, `key` and `value` for attention computation.
-        # These will then have shape `[seq_len, heads, d_k]`.
+        # Apply linear transformations
         query = self.query(query)
         key = self.key(key)
         value = self.value(value)
 
+        # Reshape to split into heads
+        # Input has shape `[seq_len, batch_size, d_model]`.
+        # We split the last dimension into `heads` and `d_k`.
+        query = query.reshape(*query.shape[:-1], self.heads, self.d_k)
+        key = key.reshape(*key.shape[:-1], self.heads, self.d_k)
+        value = value.reshape(*value.shape[:-1], self.heads, self.d_k)
+
         # Compute attention scores $Q K^\top$.
         # This gives a tensor of shape `[seq_len, seq_len, heads]`.
         # $$S_{ijh} = \sum_d Q_{ihd} K_{jhd}$$