matlab预定义函数

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1、Matlab与科学计算计算机学院刘咏梅Email:liuyongmei@hrbeu.edu.cn1第四章MATLAB编程（预定义函数）IntroductiontoMATLABMATLABBasicsofNumericalComputingMATLABProgramming(branchingandLoops)MATLABProgramming(PredefinedFunctions)MATLABGraphicandImageProcessingScientificComputingusingMATLA

2、B2本章学习的目标：IntroductiontoMatlabFunctionsbuiltinfunctionsanduserdefinedfunctionsOptionalArgumentsSharingDataUsingGlobalMemoryPreservingDataBetweenCallstoaFunctionFunctionFunctionsSubfunctions3FunctionsFunctionsaremorecomplexthanscriptsFunctionshavetheirow

3、nlocalvariablesFunctionsreturnoutputasspecified,andcanacceptinputasspecified4Whyweusefunctions?IndependentTestingofSub-Tasks:Eachtaskisanindependentunitthatcanbetestedseparately(unittesting).ReusableCode:Withinthesameprogram(thecodeisnotrepeated).Itcanb

4、eusedinanotherprogram.Isolationfromunintendedsideeffects:Isolationoffunctionvariablesfromthemainprogramvariables.Theinputandtheoutputvariablesarespecifiedclearly.5SyntaxofMatlabFunctionsUserdefinedfunctionsbehavejustlikebuiltinfunctions.Allfunctionshave

5、asimilarsyntax,whethertheyarebuilt-infunctionsoruser-definedfunctions.NameInputOutputA=cos(x)6Howtocallfunctions?Thefunctionscanbecalleddirectlyinthecommandwindow,orbyanyotherprogramorfunction.Veryimportant:iftheinputvariablesarechangedinthefunctionsthe

6、ywillnotchangeinthemainprogram(PASS-BY-VALUESCHEME)7BuiltinFunctionsBuiltinfunctionsallowustoreusecomputercodeforcalculationsthatareperformedfrequently.Forexample,supposetherewerenobuiltinsinefunctioninMATLABandyouwilldoalotoftrigonometriccalculationsin

7、volvingthesineofanangle.We’vealreadybecomefamiliarwithanumberofMATLABbuiltinfunctionslikesin(x)orplot(x,y)forexample.8SomeexamplesofBuiltinFunctionsExponential(指数)exp(x)exponentialofx(ex)sqrt(x)squarerootofxLogarithmic(对数)log(x)naturallogarithm(lnx)log1

8、0(x)log2(x)9SomeexamplesofBuiltinFunctionsNumeric(数值)fix(x)roundtonearestintegertowards0round(x)roundtonearestintegersign(x)+1,0or-1rem(x,y)Findsremainderofx/yComplex(复数)abs(x)absolutevalueangle(x)phaseangleincomplexplaneconj(x)c