斯坦福大学机器学习第一讲Lecture1Word文档格式.docx
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斯坦福大学机器学习第一讲Lecture1Word文档格式.docx
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Examples:
-Databasemining
Largedatasetsfromgrowthofautomation/web.
E.g.,Webclickdata,medicalrecords,biology,engineering-Applicationscan’tprogrambyhand.
E.g.,Autonomoushelicopter,handwritingrecognition,mostofNaturalLanguageProcessing(NLP,ComputerVision.
E.g.,Autonomoushelicopter,handwritingrecognition,mostofNaturalLanguageProcessing(NLP,ComputerVision.-Self-customizingprograms
E.g.,Amazon,Netflixproductrecommendations
Whatismachine
learning
•ArthurSamuel(1959.MachineLearning:
Fieldofstudythatgivescomputerstheabilitytolearnwithoutbeingexplicitlyprogrammed.
MachineLearningdefinition
•TomMitchell(1998Well-posedLearningProblem:
AcomputerprogramissaidtolearnfromexperienceEwithrespecttosometaskTandsomeperformancemeasureP,ifits
performanceonT,asmeasuredbyP,improveswithexperienceE.
Classifyingemailsasspamornotspam.Thenumber(orfractionofemailscorrectlyclassifiedasspam/notspam.Noneoftheabove—thisisnotamachinelearningproblem.Supposeyouremailprogramwatcheswhichemailsyoudoordonotmarkasspam,andbasedonthatlearnshowtobetterfilterspam.WhatisthetaskTinthissetting?
“AcomputerprogramissaidtolearnfromexperienceEwithrespecttosometaskTandsomeperformancemeasureP,ifitsperformanceonT,asmeasuredbyP,improveswithexperienceE.”
Classifyingemailsasspamornotspam.Supposeyouremailprogramwatcheswhichemailsyoudoordonotmarkasspam,andbasedonthatlearnshowtobetterfilterspam.WhatisthetaskTinthissetting?
Machinelearningalgorithms:
-Supervisedlearning
-UnsupervisedlearningAlsotalkabout:
Practicaladviceforapplyinglearningalgorithms.
Supervised
Learning
100
200300
4000500
150********0
Housingpriceprediction.
Price($in1000’s
Sizeinfeet2
Predictcontinuous
Breastcancer(malignant,benign
Discretevaluedoutput(0or1
Malignant?
1(Y0(N
Age-ClumpThickness--UniformityofCellShape…
Treatbothasclassificationproblems.
Treatproblem1asaclassificationproblem,problem2asaregressionproblem.Treatproblem1asaregressionproblem,problem2asaclassificationproblem.Treatbothasregressionproblems.You’rerunningacompany,andyouwanttodeveloplearningalgorithmstoaddresseachoftwoproblems.Problem1:
Youhavealargeinventoryofidenticalitems.Youwanttopredicthowmanyoftheseitemswillselloverthenext3months.Problem2:
You’dlikesoftwaretoexamineindividualcustomeraccounts,andforeachaccountdecideifithasbeenhacked/compromised.
AndrewNg
AndrewNgIntroductionUnsupervised
LearningMachineLearning
AndrewNgx1
x2
SupervisedLearning
UnsupervisedLearningx1
Genes
Individuals
OrganizecomputingclustersImagecredit:
NASA/JPL-Caltech/E.Churchwell(Univ.ofWisconsin,Madison
Cocktailpartyproblem
Microphone#1Microphone#2
Speaker#1Speaker#2
Microphone#1:
Microphone#2:
Microphone#1:
[AudioclipscourtesyofTe-WonLee.]Output#1:
Output#2:
Output#1:
AndrewNg
Cocktailpartyproblemalgorithm[W,s,v]=svd((repmat(sum(x.*x,1,size(x,1,1.*x*x'
;
[Source:
SamRoweis,YairWeiss&
EeroSimoncelli]AndrewNg
Ofthefollowingexamples,whichwouldyouaddressusinganunsupervisedlearningalgorithm?
(Checkallthatapply.Givenemaillabeledasspam/notspam,learnaspamfilter.Givenasetofnewsarticlesfoundontheweb,groupthemintosetofarticlesaboutthesamestory.Givenadatabaseofcustomerdata,automaticallydiscovermarketsegmentsandgroupcustomersintodifferentmarketsegments.Givenadatasetofpatientsdiagnosedaseitherhavingdiabetesornot,learntoclassifynewpatientsashavingdiabetesornot.
AndrewNg
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