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Machine Learning机器学习

Four exercises. The first two use how willing residents were to come to a community centre’s activities, in 24 districts, together with the share of households in public rental housing: first how much the curve may bend, then a pull that shortens or deletes slopes. The third is 48 students, hours in a writing workshop, and grades, with one line or four. The fourth is last year’s 24 forms on an overnight study room, and 12 chats from this week.四页练习。前两页用 24 个区里居民有多愿意来社区中心参加活动，以及住公屋的家庭占多少：先看曲线可以弯多少，再看把斜率缩短或删掉的拉力。第三页是 48 名学生、写作工作坊的时数和成绩，一条线或四条线。第四页是去年 24 份关于通宵自修室的反馈表，和本周 12 次聊天。

A curve can look right on the 24 districts used to draw it and miss a new set of districts drawn the same way. The two numbers under the chart are the error this year and the error next year.一条曲线可以在用来画它的 24 个区上看起来很贴，却错过按同样方式再抽的一批区。图下面的两个数，是今年偏了多少，明年又偏了多少。

Watch out.容易看错的地方。 Next year’s error on the screen was already visible while the bend or the pull was chosen. It is not a year the office has not yet looked at.屏幕上明年的误差，是在挑选弯曲或拉力时已经看见的。它不是办公室还没看过的那一年。

Labs练习

• Lab练习 Overfitting过拟合 Will this year’s curve still work on next year’s districts?今年的曲线在明年的区上还管用吗？
• Lab练习 Regularization正则化 What happens when slopes are shortened or deleted?斜率被缩短或删掉时，会发生什么？
• Glance一瞥 Group slopes分组斜率 One line for the university, or one line per faculty?全校一条线，还是每个学院一条？
• Glance一瞥 Updating a belief更新一个看法 Last year’s forms, this week’s chats, and where Monday’s note moves.去年的反馈表、本周的聊天，以及周一的说明移到哪里。

Related paths相关路径

Overfitting journey过拟合之旅 walks a straight line, a gentle curve, and a curve that bends to every district.依次走一条直线、一条缓弯，和一条弯向每一个区的曲线。Shrink the fit把拟合收一收 continues from that bend into a pull that shortens slopes, then one that can delete them.从那个弯曲继续走到缩短斜率的拉力，再走到可以删掉斜率的拉力。