外文翻译神经网络概述Word格式.docx
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NeuralNetworkIntroduction
1.Objectives
Asyoureadthesewordsyouareusingacomplexbiologicalneuralnetwork.Youhaveahighlyinterconnectedsetofsome1011neuronstofacilitateyourreading,breathing,motionandthinking.Eachofyourbiologicalneurons,arichassemblyoftissueandchemistry,hasthecomplexity,ifnotthespeed,ofamicroprocessor.Someofyourneuralstructurewaswithyouatbirth.Otherpartshavebeenestablishedbyexperience.
Scientistshaveonlyjustbeguntounderstandhowbiologicalneuralnetworksoperate.Itisgenerallyunderstoodthatallbiologicalneuralfunctions,includingmemory,arestoredintheneuronsandintheconnectionsbetweenthem.Learningisviewedastheestablishmentofnewconnectionsbetweenneuronsorthemodificationofexistingconnections.
Thisleadstothefollowingquestion:
Althoughwehaveonlyarudimentaryunderstandingofbiologicalneuralnetworks,isitpossibletoconstructasmallsetofsimpleartificial“neurons”andperhapstrainthemtoserveausefulfunction?
Theansweris“yes.”Thisbook,then,isaboutartificialneuralnetworks.
Theneuronsthatweconsiderherearenotbiological.Theyareextremelysimpleabstractionsofbiologicalneurons,realizedaselementsinaprogramorperhapsascircuitsmadeofsilicon.Networksoftheseartificialneuronsdonothaveafractionofthepowerofthehumanbrain,buttheycanbetrainedtoperformusefulfunctions.Thisbookisaboutsuchneurons,thenetworksthatcontainthemandtheirtraining.
2.History
Thehistoryofartificialneuralnetworksisfilledwithcolorful,creativeindividualsfrommanydifferentfields,manyofwhomstruggledfordecadestodevelopconceptsthatwenowtakeforgranted.Thishistoryhasbeendocumentedbyvariousauthors.OneparticularlyinterestingbookisNeurocomputing:
FoundationsofResearchbyJohnAndersonandEdwardRosenfeld.Theyhavecollectedandeditedasetofsome43papersofspecialhistoricalinterest.Eachpaperisprecededbyanintroductionthatputsthepaperinhistoricalperspective.
Historiesofsomeofthemainneuralnetworkcontributorsareincludedatthebeginningofvariouschaptersthroughoutthistextandwillnotberepeatedhere.However,itseemsappropriatetogiveabriefoverview,asampleofthemajordevelopments.
Atleasttwoingredientsarenecessaryfortheadvancementofatechnology:
conceptandimplementation.First,onemusthaveaconcept,awayofthinkingaboutatopic,someviewofitthatgivesclaritynottherebefore.Thismayinvolveasimpleidea,oritmaybemorespecificandincludeamathematicaldescription.Toillustratethispoint,considerthehistoryoftheheart.Itwasthoughttobe,atvarioustimes,thecenterofthesoulorasourceofheat.Inthe17thcenturymedicalpractitionersfinallybegantoviewtheheartasapump,andtheydesignedexperimentstostudyitspumpingaction.Theseexperimentsrevolutionizedourviewofthecirculatorysystem.Withoutthepumpconcept,anunderstandingoftheheartwasoutofgrasp.
Conceptsandtheiraccompanyingmathematicsarenotsufficientforatechnologytomatureunlessthereissomewaytoimplementthesystem.Forinstance,themathematicsnecessaryforthereconstructionofimagesfromcomputer-aidedtopography(CAT)scanswasknownmanyyearsbeforetheavailabilityofhigh-speedcomputersandefficientalgorithmsfinallymadeitpracticaltoimplementausefulCATsystem.
Thehistoryofneuralnetworkshasprogressedthroughbothconceptualinnovationsandimplementationdevelopments.Theseadvancements,however,seemtohaveoccurredinfitsandstartsratherthanbysteadyevolution.
Someofthebackgroundworkforthefieldofneuralnetworksoccurredinthelate19thandearly20thcenturies.Thisconsistedprimarilyofinterdisciplinaryworkinphysics,psychologyandneurophysiologybysuchscientistsasHermannvonHelmholtz,ErnstMuchandIvanPavlov.Thisearlyworkemphasizedgeneraltheoriesoflearning,vision,conditioning,etc.,anddidnotincludespecificmathematicalmodelsofneuronoperation.
Themodernviewofneuralnetworksbeganinthe1940swiththeworkofWarrenMcCullochandWalterPitts[McPi43],whoshowedthatnetworksofartificialneuronscould,inprinciple,computeanyarithmeticorlogicalfunction.Theirworkisoftenacknowledgedastheoriginofthe
neuralnetworkfield.
McCullochandPittswerefollowedbyDonaldHebb[Hebb49],whoproposedthatclassicalconditioning(asdiscoveredbyPavlov)ispresentbecauseofthepropertiesofindividualneurons.Heproposedamechanismforlearninginbiologicalneurons.
Thefirstpracticalapplicationofartificialneuralnetworkscameinthelate1950s,withtheinventionoftheperceptionnetworkandassociatedlearningrulebyFrankRosenblatt[Rose58].Rosenblattandhiscolleaguesbuilta