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大模型笔记：pytorch实现MOE

news 来源：原创 2025/6/17 13:18:34

0 导入库

import torch
import torch.nn as nn
import torch.nn.functional as F

1 专家模型

#一个简单的专家模型，可以是任何神经网络架构
class Expert(nn.Module):
    def __init__(self, input_size, output_size):
        super(Expert, self).__init__()
        self.fc = nn.Linear(input_size, output_size)

    
    def forward(self, x):
        return self.fc(x)

2 MOE

class MoE(nn.Module):
    def __init__(self, num_experts, input_size, output_size,topk):
        super(MoE, self).__init__()
        self.num_experts = num_experts 
        self.topk=topk
        self.experts = nn.ModuleList([Expert(input_size, output_size) for _ in range(num_experts)])
        #创建多个专家
        self.gating_network = nn.Linear(input_size, num_experts)  
        #门控网络

    def forward(self, x):
        #假设x的维度是(batch,input_size)
                   
        gating_scores = self.gating_network(x)
        # 门控网络决定权重 （选择每一个专家的概率）
        #输出维度是(batch_size, num_experts)

        topk_gate_scores,topk_gate_index=gating_scores.topk(topk,-1)
        #选取topk个专家
        #(batch_size,topk)

        gating_scores_filtered=torch.full_like(gating_scores,fill_value=float("-inf"))
        gating_scores_filtered=gating_scores_filtered.scatter(-1,topk_gate_index,topk_gate_scores)
        gating_scores_filtered=F.softmax(gating_scores_filtered,dim=-1)
        ##创建一个全为负无穷的张量 zeros，并将 topk_gate_scores 的值插入到这个张量的对应位置
        #(batch_size,num_experts)
                    
        expert_outputs = torch.stack([expert(x) for expert in self.experts], dim=1)  
        # 专家网络输出
        #每个expert的输出维度是 (batch_size, output_size)
        #stack沿着第二个维度堆叠，之后expert_outputs的维度是(batch_size,num_experts,output_size)
                   
        moe_output = torch.bmm(gating_scores_filtered.unsqueeze(1), expert_outputs).squeeze(1) 
        # 加权组合专家输出 
        #gating_scores.unsqueeze(1)——>(batch_size, 1,num_experts)
        #torch.bmm(gating_scores.unsqueeze(1), expert_outputs)——>(batch_size,1,output_size)
        #moe_output——>(batch_size,output_size)
        return moe_output

3 输入举例


input_size = 10  
# 输入特征是大小为10的向量
output_size = 5  
# 输出大小为5的向量
num_experts = 3  
# 3个专家


moe_model = MoE(num_experts, input_size, output_size)
# 初始化MOE模型


input_vector = torch.randn(1, input_size)
# 创建一个输入向量


output_vector = moe_model(input_vector)
# 前向传递


print(output_vector.shape,output_vector)
# 打印输出
'''
torch.Size([1, 5]) tensor([[ 2.7343e-04,  4.0966e-01, -3.6634e-01, -8.9064e-01,  4.0759e-01]],
       grad_fn=<SqueezeBackward1>)
'''