G-逻辑智能体-人工智能(AI)32

1、逻辑智能体 Logical Agents （知识，推理）Chapter 71“ThinkingRationally”Computational modelsofhuman“thought”processesComputational modelsofhumanbehaviorComputational systemsthat“think” rationallyComputational systemsthatbehaverationally2逻辑智能能体逻辑（基基于知识识）智能能体Logic(Knowledge-Based)agents通用知识识当前的感感知在决定动动作前推推理(infer)出

2、当前状状态的隐隐含状况况这在部分分可观察察环境中中至关重重要3要点基于知识识的智能能体Knowledge-basedagents怪兽世界界Wumpusworld逻辑Logicingeneral命题逻辑辑与一阶阶逻辑Propositional andfirst-orderlogic推理，合合法，等等价，可可满足模式推理理Reasoningpatterns归结Resolution前向/后后向链Forward/backward chaining4知识和推推理Knowledge&Reasoning知识库knowledgebase(KB):智能体所所知道的的一系列列知识根据推理的规规则（rulesofi

3、nference）由旧的事事实推出出新事实实逻辑Logic表示知识识，并进进行推理理5知识库Knowledge Base知识库:一系列语句以一种知识表示示语言的格式来表示（有有关世界界的）断断言基于知识识的智能能体:Tellitwhat it needs to know.Askitwhat to do应遵循推理的规规则由知识库库得到答答案tellask6通用的基基于知识识智能体体Generic KB-Based Agent7基于知识识智能体体的特性性能够:表示状态态和动作作综合新的的感知更新关于于世界的的内部认认识推导出世世界的隐隐含性质质推导出适适合的动动作8Mine SweeperDesi

4、gnalogical agent to playminesweeper9PEAS Analysis MineSweeperPerformancemeasure+1foreachmine correctlyidentified,-1forincorrectlyidentifyingamine,-1000forselecting alocationcontaininga mine, +1000 foridentifyingallmines.Environment9 x9board,eachsquarehas aminewith probability 0.1ActuatorsAgentcanmar

5、ka location as containingamine,canmarka location as unknown, or selecta location forviewingSensorsAgentcansensethe numberofminessurroundingadjacentlocationsAgentknowsnumberofminesremaining10怪兽问题题WumpusWorld怪兽Wumpus11怪兽问题题的PEAS描述Performancemeasure性能度量量gold:+1000,death: -1000-1perstep,-10 forusingthea

6、rrowEnvironment环境Squares adjacent to wumpusaresmellySquares adjacent to pitarebreezyGlitteriffgoldisinthesamesquareShootingkillswumpusifyou arefacingit. ItscreamsShootinguses up theonly arrowGrabbingpicksupgold if in samesquareReleasingdropsthe goldinsamesquareYoubumpifyouwalkinto awallSensors传感:Ste

7、nch, Breeze,Glitter,Bump,ScreamActuators执行:Left turn, Right turn, Forward, Grab, Release,Shoot12Wumpusworld的特征FullyObservableNo onlylocalperceptionDeterministicYesoutcomesexactly specifiedEpisodicNo thingswedohave an impact.StaticYesWumpusandPitsdonotmoveDiscreteYesSingle-agentYesWumpusisessentially

8、a naturalfeature13ExploringtheWumpusWorldTheKBinitially contains therulesoftheenvironment.1,1Thefirstperceptisnone,none,none,none,none,Move to safecelle.g. 2,12,1Breezeindicates thatthereisapitin2,2or3,1Returnto1,1totry nextsafecell14ExploringtheWumpusWorld1,2Stenchincell:wumpusisin1,3or2,2YETnotin1

9、,1Thus notin2,2orstenchwouldhavebeen detected in 2,1Thuswumpusisin1,3Thus 2,2issafe becauseoflackofbreezein1,2Thus pitin3,1Move to nextsafecell 2,215ExploringtheWumpusWorld2,2DetectnothingMove to unvisitedsafe celle.g.2,32,3Detectglitter, smell,breezeThuspick up goldThuspitin3,3or2,416What is alogic

10、?一种格式式化的语语言语法Syntax怎样的表表达是合合法的语义Semantics一个合法法的表达达式表示示什么样样的意义义逻辑中每每一条语语句的真真值都对对应着世世界里的的一种可可能例如算数数语言X+2=yisa sentence,x2+y is nota sentenceX+2=yistrue in aworldwherex=7 andy =1X+2=yisfalseina world where x=0andy=617蕴涵Entailment蕴涵Entailment意味着一一个东西西跟随另外一个个东西:KB知识库KB蕴涵语句当且仅当当KB为真的所有情况里也为真例如一一条语句句的知识识库K

11、B“the Giantswonand theReds won”蕴涵“TheGiants won”.又如,x+y=4蕴涵4=x+y蕴涵其实实就是语语句之间间基于语义的一种关关系18模型models逻辑学家家的就是是以模型的方式来来进行思思维的如果在m中为真，则m是语句的一个模型M()表示语句句的所有模模型的集集合则KB iffM(KB)M()例如KB= Giantswonand Redswon =Giants won19怪兽问题题里的蕴蕴涵Entailment in thewumpusworld为说明方方便，对对Wumpusworld进行简化化，只考考虑有关关陷阱的的模型下图为探探测到方方格1,

12、1什么都没没有，然然后向右右到方格格2,1，感知到到2,1有微风之之后的情情形 20WumpusmodelsIAllpossiblemodels (exactly 8) in thisreducedWumpusworld.PitBreeze21WumpusmodelsIIKB=怪兽世界界的规则则由感知知得到的的观察22WumpusmodelsIII1= “1,2issafe”,KB1,通过模型检验验（modelchecking）得证23WumpusmodelsIV2= 2,2issafe,KB 224推理过程程InferenceProceduresKBi即 语句句通过过程程i从KB导出可靠So

13、undness:只要KBi,就有KB为真，则称i是可靠的(推推理不会会出错，但不一一定能够够导出所所有的正正确结论论)完备Completeness:只要KB,就有KBi为真，则称i是完备的的(所有的的正确结结论都会会被导出出，但是是可能会会导出一一些多余余的错误误结论)25语义透视视图当知识库库KB为真时，由一个个可靠的的推理过过程导出出的语句也一定是是为真的的26命题逻辑辑:语法命题逻辑辑是最简简单的逻逻辑命题符号号P1, P2等，表示示语句IfS is asentence,S is asentence(negation)IfS1andS2aresentences,S1S2isa sente

14、nce(conjunction)IfS1andS2aresentences,S1S2isa sentence(disjunction)IfS1andS2aresentences,S1S2isa sentence(implication)IfS1andS2aresentences,S1S2isa sentence(biconditional)27命题逻辑辑:语义Each model/world specifiestrue or false foreach proposition symbolE.g.P1,2P2,2P3,1falsetruefalseWith these symbols, 8po

15、ssiblemodels,canbeenumeratedautomatically.Rulesforevaluatingtruthwith respecttoamodelm:Sis trueiffS is falseS1S2istrueiffS1istrueandS2istrueS1S2istrueiffS1istrueorS2istrueS1S2istrueiffS1isfalseorS2istruei.e.,isfalseiffS1istrueandS2isfalseS1S2istrueiffS1S2istrueandS2S1istrueP1,2(P2,2P3,1) =true(truefalse) =truetrue=true命题逻辑辑不要求求S1和S2之间存在在任何相相关性或或因果关关系；如如果S1为真，则则我主张张S2为真，否否则我不不做任何何声明28Truthtablesfor connectives29WumpusworldsentencesLetPi,jbetrue if there is apit in i,j.LetBi,jbetrue if there is abreeze in i,j.start:P1,1B1,1B2,1Pitscausebreezes in