//  [python]
def forward(self, x, mask = None):
        """
        Args:
            x: input features with shape of (num_windows*B, Mh*Mw, C)
            mask: (0/-inf) mask with shape of (num_windows, Wh*Ww, Wh*Ww) or None
        """
        # [batch_size*num_windows, Mh*Mw, total_embed_dim]
        B_, N, C = x.shape
        # qkv(): -> [batch_size*num_windows, Mh*Mw, 3 * total_embed_dim]
        # reshape: -> [batch_size*num_windows, Mh*Mw, 3, num_heads, embed_dim_per_head]
        # permute: -> [3, batch_size*num_windows, num_heads, Mh*Mw, embed_dim_per_head]
        qkv = self.qkv(x).reshape(B_, N, 3, self.num_heads, C // self.num_heads).permute(2, 0, 3, 1, 4)
        # [batch_size*num_windows, num_heads, Mh*Mw, embed_dim_per_head]
        q, k, v = qkv.unbind(0)  # make torchscript happy (cannot use tensor as tuple)
        attn = torch.einsum("bhqd, bhkd -> bhqk", q, k) \
                                      / torch.maximum(torch.norm(q, dim=-1, keepdim=True)
                                                      * torch.norm(k, dim=-1, keepdim=True).transpose(-2, -1),
                                                      torch.tensor(1e-06, device=q.device, dtype=q.dtype))
        # transpose: -> [batch_size*num_windows, num_heads, embed_dim_per_head, Mh*Mw]
        # @: multiply -> [batch_size*num_windows, num_heads, Mh*Mw, Mh*Mw]
        #q = q * self.scale
        # cosine -->dot?????? Scaled cosine attention：cosine(q,k)/tau 也许理解的不准确： 控制数值范围有利于训练稳定 （残差块的累加 导致深层难以稳定训练）
        # attn = (q @ k.transpose(-2, -1))
        # q = torch.norm(q, p=2, dim=-1)
        # k = torch.norm(k, p=2, dim=-1)
        # attn /= q.unsqueeze(-1)
        # attn /= k.unsqueeze(-2)
        #attn=attention_map
        #print('attn shape:',attn.size())
        #print('attn2 shape:',attention_map.size())
        attn/=self.tau.clamp(min=0.01)
        
        # relative_position_bias_table.view: [Mh*Mw*Mh*Mw,nH] -> [Mh*Mw,Mh*Mw,nH]
        # relative_position_bias = self.relative_position_bias_weight[self.relative_position_index.view(-1)].view(
        #     self.window_size[0] * self.window_size[1], self.window_size[0] * self.window_size[1], -1)
        # relative_position_bias = relative_position_bias.permute(2, 0, 1).contiguous()  # [nH, Mh*Mw, Mh*Mw]
       # print("net work new positional_enco:",self.__get_relative_positional_encodings().size())
        #print('attn shape:',attn.size())
        #attn = attn + relative_position_bias.unsqueeze(0)
        attn = attn + self.get_relative_positional_encodings()
        if mask is not None:
            # mask: [nW, Mh*Mw, Mh*Mw]
            nW = mask.shape[0]  # num_windows
            # attn.view: [batch_size, num_windows, num_heads, Mh*Mw, Mh*Mw]
            # mask.unsqueeze: [1, nW, 1, Mh*Mw, Mh*Mw]
            attn = attn.view(B_ // nW, nW, self.num_heads, N, N) + mask.unsqueeze(1).unsqueeze(0)
            attn = attn.view(-1, self.num_heads, N, N)
            attn = self.softmax(attn)
        else:
            attn = self.softmax(attn)

        attn = self.attn_drop(attn)

        # @: multiply -> [batch_size*num_windows, num_heads, Mh*Mw, embed_dim_per_head]
        # transpose: -> [batch_size*num_windows, Mh*Mw, num_heads, embed_dim_per_head]
        # reshape: -> [batch_size*num_windows, Mh*Mw, total_embed_dim]
       # x = (attn @ v).transpose(1, 2).reshape(B_, N, C)  ## float()
        x = torch.einsum("bhal, bhlv -> bhav", attn, v)
        #x = self.proj(x)
        #x = self.proj_drop(x)
        #print('out shape:',x.size())
        return x