bring in two tricks from the cogview paper for reducing the chances o…

…f overflow, for attention and layernorm

dalle2_pytorch/dalle2_pytorch.py

@@ -629,10 +629,13 @@ def __init__(
         heads = 8,
         dropout = 0.,
         causal = False,
-        rotary_emb = None
+        rotary_emb = None,
+        pb_relax_alpha = 32 ** 2
     ):
         super().__init__()
-        self.scale = dim_head ** -0.5
+        self.pb_relax_alpha = pb_relax_alpha
+        self.scale = dim_head ** -0.5 * (pb_relax_alpha ** -1)
+
         self.heads = heads
         inner_dim = dim_head * heads
 
@@ -696,6 +699,9 @@ def forward(self, x, mask = None, attn_bias = None):
 
         # attention
 
+        sim = sim - sim.amax(dim = -1, keepdim = True).detach()
+        sim = sim * self.pb_relax_alpha
+
         attn = sim.softmax(dim = -1, dtype = torch.float32)
         attn = self.dropout(attn)
 
@@ -1210,10 +1216,12 @@ def __init__(
         dim_head = 64,
         heads = 8,
         dropout = 0.,
-        norm_context = False
+        norm_context = False,
+        pb_relax_alpha = 32 ** 2
     ):
         super().__init__()
-        self.scale = dim_head ** -0.5
+        self.pb_relax_alpha = pb_relax_alpha
+        self.scale = dim_head ** -0.5 * (pb_relax_alpha ** -1)
         self.heads = heads
         inner_dim = dim_head * heads
 
@@ -1259,6 +1267,9 @@ def forward(self, x, context, mask = None):
             mask = rearrange(mask, 'b j -> b 1 1 j')
             sim = sim.masked_fill(~mask, max_neg_value)
 
+        sim = sim - sim.amax(dim = -1, keepdim = True).detach()
+        sim = sim * self.pb_relax_alpha
+
         attn = sim.softmax(dim = -1, dtype = torch.float32)
 
         out = einsum('b h i j, b h j d -> b h i d', attn, v)

dalle2_pytorch/version.py

@@ -1 +1 @@
-__version__ = '0.16.0'
+__version__ = '0.16.1'