浅探关节镜下盘状半月板损伤的治疗PPT学习教案

1、会计学1浅探关节镜下盘状半月板损伤的治疗浅探关节镜下盘状半月板损伤的治疗第1页/共67页第2页/共67页nAvoid overfitting第3页/共67页第4页/共67页第5页/共67页第6页/共67页第7页/共67页Term presentTerm absentDocument belongs to categoryABDocument does not belong to categoryCDX2 = N(AD-BC)2 / ( (A+B) (A+C) (B+D) (C+D) )Use either maximum or average X2Value for complete inde

2、pendence?第8页/共67页第9页/共67页第10页/共67页第11页/共67页第12页/共67页第13页/共67页Why is selecting common terms a good strategy?第14页/共67页第15页/共67页第16页/共67页第17页/共67页第18页/共67页第19页/共67页nNo clear examples of higher performance through dimension reduction第20页/共67页第21页/共67页nMore on this in Lecture 9 (Active Learning)第22页/共67页

3、n第23页/共67页第24页/共67页第25页/共67页第26页/共67页第27页/共67页Truth: yesTruth: noClassifier: yes1010Classifier: no10970Truth: yesTruth: noClassifier: yes9010Classifier: no10890Truth: yesTruth: noClassifier: yes10020Classifier: no201860Class 1Class 2Micro.Av. TablenMacroaveraged precision: (0.5 + 0.9)/2 = 0.7nMicroa

4、veraged precision: 100/120 = .83nWhy this difference?第28页/共67页n1.24 for docs with at least one category第29页/共67页第30页/共67页第31页/共67页53Topic assigned by classifierActual TopicThis (i, j) entry means 53 of the docs actually intopic i were put in topic j by the classifier.第32页/共67页第33页/共67页n“Correct rate

5、”: (1- error rate) Fraction of docs classified correctly:jijiiccjjiiiccjijiiiicc第34页/共67页nPrincipled approach to trainingnOptimize the measure that performance is measured withns: vector of classifier decision, z: vector of true classesnh(s,z) = cost of making decisions s for true assignments z第35页/

6、共67页Truth: yesTruth: noClassifier: yesCost:11Count:ACost:12Count:BClassifier: noCost:21Count;CCost:22Count:D第36页/共67页Truth: yesTruth: noClassifier: yes1112Classifier: no2122Most common cost: 1 for error, 0 for correct. Pi ? Product cross-sale: high cost for false positive, low cost for false negativ

7、e.Patent search: low cost for false positive, high cost for false negative.第37页/共67页第38页/共67页第39页/共67页第40页/共67页第41页/共67页第42页/共67页GovernmentScienceArts第43页/共67页第44页/共67页GovernmentScienceArts第45页/共67页第46页/共67页第47页/共67页Find a,b,c, such thatax + by c for red pointsax + by c for green points.第48页/共67页Fin

8、d a,b,c, such thatax + by c for red pointsax + by c for green points.第49页/共67页第50页/共67页In general, lots of possiblesolutions for a,b,c.第51页/共67页Support vectorsMaximizemarginnQuadratic programming problem nThe decision function is fully specified by subset of training samples, the support vectors.nText classification method du journTopic of lecture 9第52页/共67页 0.70 prime 0.67 rate 0.63 interest 0.60 rates 0.46 discount 0.43 bundesbank 0.43 baker -0.71 dlrs -0.35 world -0.33 sees -0.25 year -0.24 group -0.24 dlr -0.24 january第53页/共67页第54页/共67页?第55页/共67页第56页/共67页Posit