better init for RWKV

src/model.py

@@ -63,20 +63,15 @@ class RWKV_TimeMix(nn.Module):
         self.head_size = config.n_attn // config.n_head
 
         with torch.no_grad(): # initial time_w curves for better convergence
-            ww = torch.zeros(config.n_head, config.ctx_len)
-            curve = torch.tensor([0.9 ** (config.ctx_len - 1 - i) for i in range(config.ctx_len)])
-            curve = curve * 2 + 0.7
+            ww = torch.ones(config.n_head, config.ctx_len)
+            curve = torch.tensor([-(config.ctx_len - 1 - i) for i in range(config.ctx_len)]) # the distance
             for h in range(config.n_head):
-                if config.n_head > 1:
-                    mix_strength = 1 - 1.2 * h / (config.n_head - 1) # mix_strength from 1 to -0.2
+                if h < config.n_head - 1:
+                    decay_speed = math.pow(config.ctx_len, -(h+1)/(config.n_head-1))
                 else:
-                    mix_strength = 0.5
-                ww[h] = (1 - mix_strength) + curve * mix_strength
-                # special tweaks because of time_shift
-                ww[h][config.ctx_len - 3] = (ww[h][config.ctx_len - 3] * 2 + 1) / 3
-                ww[h][config.ctx_len - 2] = (ww[h][config.ctx_len - 2] * 1 + 2) / 3
-                ww[h][config.ctx_len - 1] = 1
-                # print(h, mix_strength, ww[h])
+                    decay_speed = 0
+                ww[h] = torch.exp(curve * decay_speed)
+                # print('layer', layer_id, 'head', h, 'decay_speed', round(decay_speed, 4), ww[h][:5].numpy(), '...', ww[h][-5:].numpy())
         self.time_w = nn.Parameter(ww)
 
         self.time_alpha = nn.Parameter(torch.ones(self.n_head, 1, config.ctx_len))