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80%；新环境中颜色一致率降到 10%，形状仍为 80%。一个只用颜色的规则在源域期望准确率为 90%、目标域为 10%；只用形状则两域都为 80%。这里没有真正训练网络，因此只能证明规则在指定分布下失效，不能声称已经测得迁移带来的负收益。","sha256":"60c3e09851226bcb5159f1fda0394bde192080355322a0673534905c9090a271","chapter":{"id":"course","title":"分布变了，源域最方便的线索可能最危险"},"unit":{"id":"notebook-blocks/0d856b8e3bd442f9bd30fd3a2b3a9d60","title":"分布变了，源域最方便的线索可能最危险"},"page":{"id":"reading-opening","title":"分布变了，源域最方便的线索可能最危险","number":1},"sectionTitle":"分布变了，源域最方便的线索可能最危险","currentQuestion":"分布变了，源域最方便的线索可能最危险","sourceSlides":[],"knowledgeBlock":null,"formulas":[],"previousBlock":"b-15a29832e94940f201f6d892","nextBlock":"b-73060f3d7197fc8fca7b90de","prerequisites":[{"id":"b-15a29832e94940f201f6d892","url":"#b-15a29832e94940f201f6d892","role":"section-title"},{"id":"b-365e111bfda722e310082fbe","url":"#b-365e111bfda722e310082fbe","role":"problem-context"}],"relatedBlocks":[]},{"id":"b-73060f3d7197fc8fca7b90de","type":"p","scope":"document","url":"https://codingai-lec03.pages.dev/course/notebook-blocks/0d856b8e3bd442f9bd30fd3a2b3a9d60.html#b-73060f3d7197fc8fca7b90de","content":"要声称**负迁移**，需要同一目标任务、标签预算、训练和评价划分下，比较源预训练初始化与合理的目标域基线，例如从头训练或其他初始化；若前者更差，差值才是当前协议下的迁移负效应。冻结、局部微调、全量微调允许不同程度改写源线索，不能仅比较训练准确率。若目标标签很少，全量更新还可能把小样本噪声写进整个网络。","sha256":"b655be870fde80e77afd34b140e3a1a1938336d19183cb649e78ee4e026567d1","chapter":{"id":"course","title":"分布变了，源域最方便的线索可能最危险"},"unit":{"id":"notebook-blocks/0d856b8e3bd442f9bd30fd3a2b3a9d60","title":"分布变了，源域最方便的线索可能最危险"},"page":{"id":"reading-opening","title":"分布变了，源域最方便的线索可能最危险","number":1},"sectionTitle":"分布变了，源域最方便的线索可能最危险","currentQuestion":"分布变了，源域最方便的线索可能最危险","sourceSlides":[],"knowledgeBlock":null,"formulas":[],"previousBlock":"b-595d7d2de136cf1e40c80c86","nextBlock":"b-dc2250e23131e53f08b5d467","prerequisites":[{"id":"b-15a29832e94940f201f6d892","url":"#b-15a29832e94940f201f6d892","role":"section-title"},{"id":"b-365e111bfda722e310082fbe","url":"#b-365e111bfda722e310082fbe","role":"problem-context"}],"relatedBlocks":[]},{"id":"b-dc2250e23131e53f08b5d467","type":"p","scope":"document","url":"https://codingai-lec03.pages.dev/course/notebook-blocks/0d856b8e3bd442f9bd30fd3a2b3a9d60.html#b-dc2250e23131e53f08b5d467","content":"随机划分若同时把同一背景、拍摄设备或主体身份分进两侧，可能隐藏域变化。按环境或主体分组的保留集更接近“到新场景使用”的问题；验证集仍须用于选择适配强度，不能看完测试环境再挑出最好的一种方法。[D2L：环境与分布偏移](https://d2l.ai/chapter_linear-classification/environment-and-distribution-shift.html) 给出这些假设变化的基础讨论。[LAB 19](https://deepnote.com/workspace/ise3309jingao-5ba66b0a-4283-4f5a-ae06-3f68d3201e99/project/38755e4e-23f6-4f5f-8c68-8a2e4114b1c1/notebook/c20ef6a65d184331b1b52bf351077504?utm_source=openai&utm_medium=mcp&utm_campaign=openaimcp&utm_content=c20ef6a65d184331b1b52bf351077504&utm_term=get_notebook) 的真实逻辑回归与适配比较（输入为两维解析特征，不是照片）和 [LAB 02](https://deepnote.com/workspace/ise3309jingao-5ba66b0a-4283-4f5a-ae06-3f68d3201e99/project/38755e4e-23f6-4f5f-8c68-8a2e4114b1c1/notebook/4bd450d54870432db91c80a4df563b8e?utm_source=openai&utm_medium=mcp&utm_campaign=openaimcp&utm_content=4bd450d54870432db91c80a4df563b8e&utm_term=get_notebook) 的实际参数迁移各承担其中一层证据。","sha256":"d622785e68c1be46b0cab51204b3da00c5c09a4111af63a00a58898ce3ad502c","chapter":{"id":"course","title":"分布变了，源域最方便的线索可能最危险"},"unit":{"id":"notebook-blocks/0d856b8e3bd442f9bd30fd3a2b3a9d60","title":"分布变了，源域最方便的线索可能最危险"},"page":{"id":"reading-opening","title":"分布变了，源域最方便的线索可能最危险","number":1},"sectionTitle":"分布变了，源域最方便的线索可能最危险","currentQuestion":"分布变了，源域最方便的线索可能最危险","sourceSlides":[],"knowledgeBlock":null,"formulas":[],"previousBlock":"b-73060f3d7197fc8fca7b90de","nextBlock":"b-ff2c8da6b36e4c4f6f6f87b5","prerequisites":[{"id":"b-15a29832e94940f201f6d892","url":"#b-15a29832e94940f201f6d892","role":"section-title"},{"id":"b-365e111bfda722e310082fbe","url":"#b-365e111bfda722e310082fbe","role":"problem-context"}],"relatedBlocks":[]},{"id":"b-ff2c8da6b36e4c4f6f6f87b5","type":"p","scope":"document","url":"https://codingai-lec03.pages.dev/course/notebook-blocks/0d856b8e3bd442f9bd30fd3a2b3a9d60.html#b-ff2c8da6b36e4c4f6f6f87b5","content":"第一条主线到这里形成一个闭环：重建规定要保留什么，对比规定哪些变化要忽略，教师规定向谁靠近，而读出与新域评价检查这些选择是否支持使用。下一册 [CLS 07](https://deepnote.com/workspace/ise3309jingao-5ba66b0a-4283-4f5a-ae06-3f68d3201e99/project/38755e4e-23f6-4f5f-8c68-8a2e4114b1c1/notebook/586e66e049764158a50747e69c219312?utm_source=openai&utm_medium=mcp&utm_campaign=openaimcp&utm_content=586e66e049764158a50747e69c219312&utm_term=get_notebook) 改变的不是标签供给，而是输出要求：即使整图类别判断正确，网络还要交付对象在哪里。","sha256":"12bcd5d53dcdcdd3a25813b2723f5fe32ed93be252405fcf1d9df668daa7d8a8","chapter":{"id":"course","title":"分布变了，源域最方便的线索可能最危险"},"unit":{"id":"notebook-blocks/0d856b8e3bd442f9bd30fd3a2b3a9d60","title":"分布变了，源域最方便的线索可能最危险"},"page":{"id":"reading-opening","title":"分布变了，源域最方便的线索可能最危险","number":1},"sectionTitle":"分布变了，源域最方便的线索可能最危险","currentQuestion":"分布变了，源域最方便的线索可能最危险","sourceSlides":[],"knowledgeBlock":null,"formulas":[],"previousBlock":"b-dc2250e23131e53f08b5d467","nextBlock":null,"prerequisites":[{"id":"b-15a29832e94940f201f6d892","url":"#b-15a29832e94940f201f6d892","role":"section-title"},{"id":"b-365e111bfda722e310082fbe","url":"#b-365e111bfda722e310082fbe","role":"problem-context"}],"relatedBlocks":[]}]}