diff --git a/llms/mlx_lm/models/mamba2.py b/llms/mlx_lm/models/mamba2.py index 09e650cd..a2f014e5 100644 --- a/llms/mlx_lm/models/mamba2.py +++ b/llms/mlx_lm/models/mamba2.py @@ -117,6 +117,7 @@ class Mamba2Block(nn.Module): shape=(self.n_heads,) ) ) + dt = mx.clip(dt, args.time_step_floor, float('inf')) inv_dt = dt + mx.log(-mx.exp(-dt) + 1) # Inverse softplus self.dt_bias = mx.array(inv_dt) @@ -146,63 +147,58 @@ class Mamba2Block(nn.Module): def __call__(self, u: mx.array, cache=None): batch_size, seq_len, _ = u.shape - - # Project input - zxbcdt = self.in_proj(u) # (B, L, d_in_proj) - # Split projections - z = zxbcdt[..., :self.d_inner] + # Project input + zxbcdt = self.in_proj(u) + z = zxbcdt[..., :self.d_inner] xBC = zxbcdt[..., self.d_inner:self.d_inner + (self.d_inner + 2 * self.n_groups * self.d_state)] dt = zxbcdt[..., -self.n_heads:] - - # Process time steps - simplified to match PyTorch - dt = nn.softplus(dt + self.dt_bias) # (B, L, nheads) - xBC, conv_state = self.conv1d(xBC, cache[0] if cache else None) # (B, L, self.d_inner + 2 * ngroups * d_state) + # Process dt + dt = nn.softplus(dt + self.dt_bias) + + # Conv1d and activation + xBC, conv_state = self.conv1d(xBC, cache[0] if cache else None) if cache is not None: cache[0] = conv_state xBC = silu(xBC) - xBC = xBC[:, :seq_len, :] # Split conv output and reshape x = xBC[..., :self.d_inner] - B = mx.reshape(xBC[..., self.d_inner:self.d_inner + self.n_groups * self.d_state], (batch_size, seq_len, self.n_groups, -1)) - C = mx.reshape(xBC[..., -self.n_groups * self.d_state:], (batch_size, seq_len, self.n_groups, -1)) + B = mx.reshape(xBC[..., self.d_inner:self.d_inner + self.n_groups * self.d_state], + (batch_size, seq_len, self.n_groups, -1)) + C = mx.reshape(xBC[..., -self.n_groups * self.d_state:], + (batch_size, seq_len, self.n_groups, -1)) - # Reshape for SSM processing x = mx.reshape(x, (batch_size, seq_len, self.n_heads, self.d_head)) # Initialize state if cache and cache[1] is not None: - # State initialization might need proper scaling prev_state = cache[1] else: prev_state = mx.zeros((batch_size, self.n_heads, self.d_head, self.d_state)) - - # Compute dA - simplified to match PyTorch + + # Compute dA A = -mx.exp(self.A_log) dt = mx.reshape(dt, (batch_size, seq_len, self.n_heads)) dA = mx.exp(dt * mx.expand_dims(A, axis=(0, 1))) - # Process sequence + # Process sequence next_state = prev_state outputs = [] for t in range(seq_len): - # Get current step tensors - xt = x[:, t] # [batch, n_heads, d_head] - Bt = B[:, t] # [batch, n_heads, d_state] - Ct = C[:, t] # [batch, n_heads, d_state] - dAt = dA[:, t] # [batch, n_heads] + xt = x[:, t] + Bt = B[:, t] + Ct = C[:, t] + dAt = dA[:, t] - # Compute dBx using einsum to match PyTorch - dBx = mx.einsum('bh,bgd,bhp->bhpd', dAt, Bt, xt) # dAt: (b,h), Bt: (b,g,d), xt: (b,h,p) -> (b,h,p,d) - # Update state + dBx = mx.einsum('bh,bgd,bhp->bhpd', dAt, Bt, xt) next_state = next_state * mx.expand_dims(dAt, axis=(-1, -2)) + dBx - - # Compute output with groups + + # Compute output yt = mx.einsum('bhpd,bgd->bhp', next_state, Ct) yt = yt + xt * mx.expand_dims(self.D, -1) @@ -214,7 +210,7 @@ class Mamba2Block(nn.Module): # Update cache if cache is not None: cache[1] = next_state - + return mx.concatenate(outputs, axis=1)