修正: deepseek 笔记 96 处块级公式改为多行写法(适配 SilverBullet 行首锚点), 索引脚本同步 _abstract 命名
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MoE 层替换前馈网络(FFN),每层含多个结构相同的专家,词元按亲和度只被分配给其中一部分。第 $l$ 层第 $t$ 个词元的输出为
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$$\mathbf{h}_{t}^{l}=\sum_{i=1}^{N}\left(g_{i,t}\text{FFN}^{n}_{i}(\mathbf{u}_{t}^{l})\right)+\mathbf{u}_{t}^{l},\qquad s_{i,t}=\text{Softmax}_{i}\left(\mathbf{u}_{t}^{l\top}\mathbf{e}_{i}^{l}\right)$$
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$$
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\mathbf{h}_{t}^{l}=\sum_{i=1}^{N}\left(g_{i,t}\text{FFN}^{n}_{i}(\mathbf{u}_{t}^{l})\right)+\mathbf{u}_{t}^{l},\qquad s_{i,t}=\text{Softmax}_{i}\left(\mathbf{u}_{t}^{l\top}\mathbf{e}_{i}^{l}\right)
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$$
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其中 $N$ 为专家总数,$g_{i,t}=s_{i,t}$ 当且仅当它进入 TopK 集合,否则为 0。DeepSeekMoE 另引入细粒度专家切分与共享专家隔离(共享专家处理所有词元、承载公共知识):
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$$\mathbf{h}_{t}^{l}=\sum_{i=1}^{K_{s}}\text{FFN}^{s}_{i}(\mathbf{u}_{t}^{l})+\sum_{i=1}^{N}\left(g_{i,t}\text{FFN}^{n}_{i}(\mathbf{u}_{t}^{l})\right)+\mathbf{u}_{t}^{l}$$
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$$
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\mathbf{h}_{t}^{l}=\sum_{i=1}^{K_{s}}\text{FFN}^{s}_{i}(\mathbf{u}_{t}^{l})+\sum_{i=1}^{N}\left(g_{i,t}\text{FFN}^{n}_{i}(\mathbf{u}_{t}^{l})\right)+\mathbf{u}_{t}^{l}
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$$
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其中 $K_{s}$ 为共享专家数。
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@@ -42,17 +46,23 @@ $$\mathbf{h}_{t}^{l}=\sum_{i=1}^{K_{s}}\text{FFN}^{s}_{i}(\mathbf{u}_{t}^{l})+\s
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**专家相关性评分**:给出两种基于词元亲和度的度量。平均门控分数(ESFT-Gate)衡量专家对采样数据的平均亲和度:
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$$g_{i}^{l}=\frac{1}{N_{s}}\sum_{j=1}^{N_{s}}\frac{1}{L_{j}}\sum_{k=1}^{L_{j}}g_{i,k}^{l}$$
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$$
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g_{i}^{l}=\frac{1}{N_{s}}\sum_{j=1}^{N_{s}}\frac{1}{L_{j}}\sum_{k=1}^{L_{j}}g_{i,k}^{l}
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$$
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词元选择比例(ESFT-Token)衡量专家被选中的词元占比:
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$$r_{i}^{l}=\frac{1}{N_{s}}\sum_{j=1}^{N_{s}}\frac{1}{L_{j}}\sum_{k=1}^{L_{j}}\frac{\mathbb{1}\left(g_{i,k}^{l}>0\right)}{K}$$
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$$
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r_{i}^{l}=\frac{1}{N_{s}}\sum_{j=1}^{N_{s}}\frac{1}{L_{j}}\sum_{k=1}^{L_{j}}\frac{\mathbb{1}\left(g_{i,k}^{l}>0\right)}{K}
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$$
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其中 $\mathbb{1}(\cdot)$ 为指示函数、$K$ 为每词元激活的专家数;前者看亲和度强弱,后者看调用频率。
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**专家选择与微调**:每层设阈值 $p\in(0,1]$,把专家按评分从高到低累加,直到累计占比超过 $p$,得到该层待训练专家集合 $E_{s}^{l}$:
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$$\sum_{i\in E_{s}^{l}}R_{i}^{l}\geqslant p,\qquad R_{i}^{l}\in\{r_{i}^{l},\ g_{i}^{l}\}$$
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$$
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\sum_{i\in E_{s}^{l}}R_{i}^{l}\geqslant p,\qquad R_{i}^{l}\in\{r_{i}^{l},\ g_{i}^{l}\}
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$$
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关键:训练与推理时词元仍可路由到任意专家,但只有 $E_{s}^{l}$ 内专家会被更新,其余专家与模块全部冻结——既保留路由能力与专精结构,又把可训练参数压到极小。
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