【5A文】人工智能不确定推理推理概述与概率论基础.ppt

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1、Chapter4UncertaintyReasoning不确定推理ThelimitationofFOLFOL的局限性一阶逻辑作为形式语言存在局限性，其远远不能表示人类自然语言所能表达的全部知识，而人类所认识的知识类比自然语言所能表达的知识类还多。因此一阶逻辑所能表示的知识范围十分有限。从思维推理的角度看，一阶谓词逻辑所体现的逻辑推理规律，只能用来模拟人类的部分逻辑思维现象，也远远不能代表人类逻辑思维的全部。因此各种非规范逻辑的研究很有必要。FOL过分抽象和简单，二值逻辑(childrenworld)。经典集合论:4.

2、1Overview“Uncertaintyreasoning”refersinageneralwaytoproblemsdiscussedbythatsubsetoftheAIcommunityinterestedinrepresentingandreasoningwithknowledgethatcannotbeexpressedascertainties.Therangeofproblemsdiscussedrunsthegamutfromfundamentalphilosophicalinquiryintothe

3、natureofuncertaintyandhow(ifatall)itcanbemeasuredandmodelled,topracticalperformanceissuesarisingfromthe(automatic)constructionofreal-worldmodelsandmakinginferencesfromsuchmodels.不确定性是普遍存在的，是现实世界的本质属性。人类的实践和认识活动并不仅仅在于追求确定性，更重要的是消除不确定性。不确定性渗透在人类的思想、行动之中，是各种理论的前提和基

4、础。不确定性根源于客观事物或过程自身和认识主体以及认识主体与客体之间的复杂关系中，具有本体论与认识论的含义。4.1.1ThesourcesofuncertaintyObjectiveuncertaintyRandomness(随机性)Cointossing,dietossing,lotteries,etc.Fuzziness(模糊性)Tall,beautiful,young,etc.SubjectiveuncertaintyAmbiguity(歧义性)Incompleteness(不完全)Inexactness(不精确

5、)Unreliability(不可靠)Inconsistency(不一致)UncertaintyinRulesRuleConclusionPremiseErrorEvidencecombinationParameterErrorParameter4.1.2Thefundamentalissuesofuncertaintyreasoning1.Representationissue(表示问题)Evidenceuncertainty(E,C(E))Ruleuncertainty(EH,f(H,E))2.Computat

6、ionissue（计算问题）EvidencecombinationPropagationalgorithmofuncertaintyThecompositionofconclusionuncertainty3.Semanticissue（语义问题）Themeaningofaboverepresentation&computation4.1.3TheclassificationofuncertaintyreasoningmethodFoundationofprobability概率论基础Randomevents随机事件

7、ThemeaningofprobabilityProbabilityprovidesameasureofuncertaintyassociatedwiththeoccurrenceofeventsoroutcomes–ModelsandtheoryProbability-meaningclassicalfrequentistsubjective(personal)ClassicaldefinitionIfaneventcanoccurinNmutuallyexclusive,equallylikelyways,andi

8、fmofthesepossesscharacteristicE,thentheprobabilityP(E)isequaltom/N.Example:Whatistheprobabilityofrollingatotalof7ontwodice?FrequencydefinitionIfaprocessoranexperiment