matlab应用外文翻译

IntroductiontoMATLAB

MATLAB(shortforMatrixLaboratory)isaspecial-purposecomputerprogram

optimizedtoperformengineeringandscientificcalculations.Itstartedlifehasa

programdesignedtoperformmatrixmathematics,butovertheyearsithasgrown

intoaflexiblecomputingsystemcapableofsolvingessentiallyanytechnical

problem.

TheMATLABprogramimplementstheMATLABprogramminglanguageand

providesanextensivelibraryofpredefinedfunctionsthatmaketechnical

programmingtaskseasierandmoreefficient.ThisbookintroducestheMATLAB

languageandshowshowtouseittosolvetypicaltechnicalproblems.

MATLABisahugeprogram,withanincrediblyrichvarietyoffunctions.Even

thebasicversionofMATLABwithoutanytoolkitsismuchricherthanother

technicalprogramminglanguages.Therearemorethan1000functionsinthe

basicMATLABproductalone,andthetoolkitsextendthiscapabilitywithmany

morefunctionsinvariousspecialties.Thisbookmakesnoattempttointroducethe

usertoallofMALTLAB'sowntoolstolocatethecorrectfunctionforaspecific

purposefromtheenormouschoiceavailable.

AdvantagesofMATLAB

MATLABhasmanyadvantagescomparedwithconventionalcomputer

languagesfortechnicalproblemsolving.Amongthemarethefollowing:

1.EaseofUse

MATLABisaninterpretedlanguage,likemanyversionsofBasic.LikeBasic,itis

veryeasytouse.Theprogramcanbeusedasascratchpadtoevaluate

expressionstypedatthecommandline,oritcanbeusedtoexecutelarge

prewrittenprograms.Programsmaybeeasilywrittenandmodifiedwiththe

built-inintegrateddevelopmentenvironment,anddebuggedwiththeMATLAB

debugger.Becausethelanguageissoeasytouse,itisidealforeducationaluse,

andfortherapidprototypingofnewprograms.

Manyprogramdevelopmenttoolsareprovidedtomaketheprogrameasyto

use.aworkspacebrowser,andextensivedemos.

2.Platformindependence

MATLABissupportedonmanydifferentcomputersystems,providingalarge

measureofplatformindependence.Atthetimeofthiswriting,thelanguageis

supportedonwindows9x/NT/2000andmanydifferentversionsofUNIX.

Programswrittenonanyplatformwillrunonalloftheotherplatforms,anddata

fileswrittenonanyplatformmaybereadtransparentlyonanyotherplatforms,AS

dresult,

ProgramswritteninMATLABcanmigratetonewplatformswhentheneedsof

theuserchange.

3.PredefinedFunctions

MATLABcomescompletewithanextensivelibraryofpredefinedfunctions

thatprovidetestedandprepackagedsolutionstomanybasictechnicaltasks.For

example,supposethatyouarewritingaprogramthatmustcalculatethestatistics

associatedwithaninputdataset.Inmostlanguages,youwouldneedtowriteyour

ownsubroutinesorfunctionstoimplementcalculationssuchasthearithmetic

mean,standarddeviation,median,andsoforth.Theseandhundredsofother

functionsarebuiltrightintotheMATLABlanguage,makingyourjobmucheasier.

InadditiontothelargelibraryoffunctionsbuiltintothebasicMATLAB

language,manyspecial-purposetoolboxesareavailabletohelpsolvecomplex

problemsinspecificareas.Forexample,ausercanbuystandardtoolboxesto

solveproblemsinSignalProcessing,ControlSystems,Communications,Image

Processing,andNeuralNetworks,amongmanyothers.Thereisalsoanextensive

collectionoffreeuser-contributedMATLABprogramsthataresharedthroughthe

MATLABWebsite.

4.Device-IndependentPlotting

Unlikemostothercomputerlanguages,MATLABhasmanyintegralplotting

andimagingcommands.Theplotsandimagescanbedisplayedonanygraphical

outputdevicesupportedbythecomputeronwhichMATLABisrunning.This

capabilitymakesMATLABanoutstandingtoolforvisualizingtechnicaldata.

5.GraphicalUserInterface

MATLABincludestoolsthatallowaprogrammertointeractivelyconstructa

graphicaluserinterface(GUI)forhisorherprogram.Withthiscapability,the

programmercandesignsophisticateddataanalysisprogramsthatcanbe

operatedbyrelativelyinexperiencedusers.

6.MATLABCompiler

MATLAB'sflexibilityandplatformindependenceisachievedbycompiling

MATLABprogramsintoadevice-independencep-code,andtheninterpretingthe

p-codeinstructionsatruntime.ThisapproachissimilartothatusedbyMicrosoft

isVisualBasiclanguage.Unfortunately,theresultingprogramscansometimes

executeslowlybecausetheMATLABcodeisinterpretedratherthancompiled.We

willpointoutfeaturesthattendtoslowprogramexecutionwhenweencounter

them.

AseparateMATLABcompilerisavailable.ThiscompilercancompileaMATLAB

programintoatrueexecutablethatrunsfasterthantheinterpretedcode.Itisa

greatwaytoconvertaprototypeMATLABprogramintoanexecutablesuitablefor

saleanddistributiontousers.

DisadvantagesofMATLAB

MATLABhastwoprincipaldisadvantages.Thefirstisthatitisaninterpreted

language,andthereforecanexecutemoreslowlythancompiledlanguages.This

problemcanbemitigatedbyproperlystructuringtheMATLABprogramandby

theuseoftheMATLABcompilertocompilethefinalMATLABprogrambefore

distributionandgeneraluse.

Theseconddisadvantageiscost:AfullcopyofMATLABis5to10timesmore

expensivethanaconventionalCorFortrancompiler.Thisrelativelyhighcostis

morethanoffsetbythereducedtimerequiredforanengineerorscientistto

createaworkingprogram,soMATLABiscost-effectiveforbusinesses.However,it

istooexpensiveformostindividualstoconsiderpurchasing.Fortunately,thereis

alsoaninexpensiveStudentEditionofMATLAB,whichisagreattoolforstudents

wantingtolearnthelanguage.TheStudentEditionofMATLABisessentially

identicaltothefulledition.

Withtheintroductionofbranchesandloops,ourprogramsaregoingto

becomemorecomplex,anditwillgeteasiertomakemistakes.Tohelpavoid

programmingerrors,wewillintroduceaformalprogramdesignprocedurebased

onthetechniqueknownastop-downdesign.Wewillalsointroduceacommon

algorithmdevelopmenttoolknownaspseudocode.

IntroductionToTop-DownDesignTechniques

Supposethatyouareanengineerworkinginindustry,andthatyouneedto

writeaprogramtosolvesomeproblem.Howdoyoubegin?

Whengivenanewproblem,thereisanaturaltendencytositdownata

keyboardandstartprogrammingwithout“wasting“alotoftimethinkingabout

theproblemfirst.Itisoftenpossibletogetawaywiththis“onthefly“approach

toprogrammingforverysmallproblems,suchasmanyoftheexamplesinthis

book.Intherealworld,however,problemsarelarger;andaprogrammer

attemptingthisapproachwillbecomehopelesslyboggeddown.Forlarger

problems,itpaystocompletelythinkouttheproblemandtheapproachyouare

goingtotaketoitbeforewritingasinglelineofcode.

Weintroduceaformalprogramdesignprocessinthissection,andthenapply

thatprocesstoeverymajorapplicationdevelopedintheremainderofthebook.

Forsomeofthesimpleexamplesthatwewillbedoing,thedesignprocesswill

seemlikeoverkill;however,astheproblemsthatwesolvegetlargerandlarger,the

processbecomesmoreandmoreessentialtosuccessfulprogramming.

WhenIwasanundergraduate,oneofmyprofessorswasfondofsaying,

“programmingiseasy.Itisknowingwhattoprogramthatishard."hispointwas

forcefullydrivenhometomeafterIleftuniversityandbeganworkinginindustry

onlargerscalesoftwareprojects.Ifoundthatthemostdifficultportofmyjobwas

tounderstandtheproblemIwastryingtosolve.OnceIreallyunderstoodthe

problem,itbecameeasytobreaktheproblemapartintosmaller,moreeasily

manageablepieceswithwell-definedfunctions,andthentotacklethosepieces

oneatatime.

Top-downdesignistheprocessofstartingwithalargetaskandbreakingit

downintosmaller,moreeasilyunderstandablepieces,whichperformaportionof

thedesiredtask.Eachsubtaskmayinturnbesubdividedintosmallersubtasksif

necessary.Oncetheprogramisdividedintosmallpieces,eachpiececanbecoded

andtestedindependently.Wedonotattempttocombinethesubtasksintoa

completetaskuntileachofthesubtaskshasbeenverifiedtoworkproperlyby

itself.

Theconceptoftop-downdesignisthebasisofourformalprogramdesign

process.Wewillnowintroducethedetailsoftheprocess,whichisillustratedin

figure1thestepsinvolvedare:

1.Clearlystatetheproblemthatyouaretryingtosolve.

Programsareusuallywrittentofillsomeperceivedneed,butthatneedmay

notbearticulatedclearlybythepersonrequestingtheprogram.Forexample,a

usermayaskforaprogramtosolveasystemofsimultaneouslinearequations.

Thisrequestisnotclearenoughtoallowaprogrammertodesignaprogramto

meettheneed;heorshemustfirstknowmuchmoreabouttheproblemtobe

solved.Isthesystemofequationstobesolvedrealorcomplex?Whatisthe

maximumnumberofequationsandunknownthattheprogrammusthandle?Are

thereanysymmetryintheequationsthatmightbeexploitedtomakethetask

easier?Theprogramdesignerwillhavetotalkwiththeuserrequestingthe

program,andthetwoofthemwillhavecomeupwithaclearstatementofexactly

whattheyaretryingtoaccomplish.Aclearstatementoftheproblemwillprevent

misunderstandings,anditwillalsohelptheprogramdesignertoproperly

organizehisorherthoughts.Intheexamplewev/eredescribing,aproper

statementoftheproblemmighthavebeen:

FgS

Figure1

Designandwriteaprogramtosolveasystemofsimultaneouslinear

equationshavingrealcoefficientsandwithupto20equationsin20unknowns.

2.Definetheinputsrequiredbytheprogramandtheoutputstobeproduced

bytheprogram.

Theinputstotheprogramandtheoutputsproducedbytheprogrammustbe

specifiedsothatthenewprogramwillproperlyfitintotheoverallprocessing

scheme.Inthisexample,thecoefficientsoftheequationstobesolvedare

probablyinsomepre-existingorder,andournewprogramneedstobeableto

readtheminthatorder.Andournewprogramneedstobeabletoreadthemin

thatorder.Similarly,itneedstoproducetheanswersrequiredbytheprograms

thatmayfollowitintheoverallprocessingscheme,andtowriteoutthoseanswers

intheformatneededbytheprogramsfollowingit.

3.Designthealgorithmthatyouintendtoimplementintheprogram.

Analgorithmisastep-by-stepprocedureforfindingthesolutiontoaproblem.

Itisatthisstageintheprocessthattop-downdesigntechniquescomeintoplay.

Thedesignerlooksforlogicaldivisionswithintheproblem,anddividesitupinto

subtasksalongthoselines.Thisprocessiscalleddecomposition.Ifthesubtasks

arelarge,thedesignercanbreakthemupintoevensmallersub-tasks.Thisprocess

continuesuntiltheproblemhasbeendividedintorranysmallpieces,eachof

whichdoesasimple,clearlyunderstandablejob.

Aftertheproblemhasbeendecomposedintosmallpieces,eachpieceis

furtherrefinedthroughaprocesscalledstepwiserefinement.Instepwise

refinement,adesignerstartswithageneraldescriptionofwhatthepieceofcode

shoulddo,andthendefinesthefunctionsofthepieceingreaterandgreaterdetail

untiltheyarespecificenoughtobeturnedintoMATLABstatements.Stepwise

refinementisusuallydonewithpseudocode,whichwillbedescribedinthe

nextsection.

Itisoftenhelpfultosolveasimpleexampleoftheproblembyhandduringthe

algorithmdevelopmentprecess.Ifthedesignerunderstandsthestepsthatheor

shewentthroughinsolvingtheproblembyhand,thenheorshewillbebetter

abletoapplydecompositionandstepwiserefinementtotheproblem.

4.TurnthealgorithmintoMATLABstatements.

Ifthedecompositionandrefinementprocesswascarriedoutproperly,this

stepwillbeverysimple.Alltheprogrammerwillhavetodoistoreplacepseudo

codewiththecorrespondingMATLABstatementsonaone-for-onebasis.

5.TesttheresultingMATLABprogram

ThisstepistherealIdler.Thecomponentsoftheprogrammustfirstbetested

individually,ifpossible,andthentheprogramasawholemustbetested.When

testingaprogram,wemustverifythatitworkscorrectlyforalllegalinputdatasets.

Itisverycommonforaprogramtobewritten,testedwithsomestandarddataset,

andreleasedforuse,onlytofindthatitproducesthewronganswers(orcrashes)

withadifferentinputdataset.Ifthealgorithmimplementedinaprogramincludes

differentbranches,wemusttestallofthepossiblebranchestoconfirmthatthe

programoperatescorrectlyundereverypossiblecircumstance.

Largeprogramstypicallygothroughaseriesoftestsbeforetheyarereleased

forgeneraluse(seeFigure2).Thefirststageoftestingissometimescalledunit

testing.Duringunittesting,theindividualsubtasksoftheprogramaretested

separatelytoconfirmthattheyworkcorrectly.Aftertheunittestingiscompleted,

theprogramgoesthroughaseriesofbuilds,duringwhichtheindividualsubtasks

arecombinedtoproducethefinalprogram.Thefirstbuildoftheprogram

typicallyincludesonlyafewofthesubtasks.Itisusedtochecktheinteractions

amongthosesubtasksandthefunctionsperformedbythecombinationsofthe

subtasks.Insuccessivebuilds,moreandmoresubtasksareadded,untiltheentire

programiscomplete.Testingisperformedoneachbuild,andanyerrors(bugs)

detectedarecorrectedbeforemovingontothenextbuild.

Figure2

MATLAB介绍

MATLAB（矩阵实验室的简称）是一种专业的计算机程序，用于工程科学的矩阵数学运

算。但在以后的几年内，它逐渐发展为一种极其灵活的计算体系，用于解决各种重要的技

术问题。

MATLAB程序执行MATLAB语言，并提供了一个极其广泛的预定义函数库，这样就

使得技术，作变得简单高效。本书将介绍MATLAB语言，并向大家展示如何运用它去解决

经典的技术问题。

MATLAB是一个庞大的程序，拥有难以置信的各种丰富的函数；即使基本版本的

MATLAB语言拥有的函数也比其他的工程编程语言要丰富的多。基本的MATLAB语言已

经拥有了超过1000多个函数，而它的工具包带有更多的函数，由此扩展了它在许多专业

领域的能力。本书无意将MATLAB的所有函数介绍给大家,而是让大家掌握编写调试和优

化程序的基本功，还有一些重要函数的子集。所以从大量可利用的函数中筛选出你所需要

的函数就显得尤为重要。

MATLAB的优点

MATLAB语言相对于传统的科技编程语言有诸多的优点。主要包括：

1.易用性

MATLAB是种解释型语言，就像各种版本的BASIC。和BASIC一样，它简单易用程

序可用作便笺簿求打在命令行处表达式的值，也可执行预先写好的大型程序。在MATLAB

集成开发环境下，程序可以方便的编写，修改和调试。这是因为这种语言极易使用，对于

教育应用和快速建立新程序的原型，它是一个理想的工具。许多的编程工具使得MATLAB

十分简单易用。这些工具包括：一个集成的编译/调试器，在线文件手册，工作台和扩展范

例。

2.平台独立性

MATLAB支持许多的操作系统，提供了大量的平台独立的措施。在本书编写的时侯,

windows98/2000/NT和许多版本的UNIX系统都支持它。在一个平台上编写的程序，在

其它平台上一样可以正常运行，在一个平台上编写的数据文件在其它平台上一样可以编译。

因此用户可以根据需要把MATLAB编写的程序移植到新平台。

3.预定义函数

MATLAB带有一个极大的预定义函数库，它提供了许多已测试和打包过的基本工程问

题的函数。例如，假设你正在编写一个程序，这个程序要求你必须计算与输入有关的统计

量。在许多的语言中，你需要写出你所编数组的下标和执行计算所需要的函数，这些函数

包括其数学意义，中值，标准误差等。像这样成百上千的函数已经在MATLAB中编写好,

所以让编程变得更加简单。

除了植入MATLAB基本语言中的大量函数，还有订多专用工具箱，以帮助用户解次在

具体领域的复杂问题。例如，用户可以购买标准的工具箱以解决在信号处理，控制系统，

通信，图象处理，神经网络和其他许多领域的问题。

4.机制独立的画图

与其他语言不同,MATLAB有许多的画图和图象处理命令。当MATLAB运行时，这

些标绘图和图片将会出现在这台电脑的图像输出设备中。此功能使得MATLAB成为一个形

象化技术数据的卓越工具。

5.用户图形界面

MATLAB允许程序员为他们的程序建立一个交互式的用户图形界面。利用MATLAB

的这种功能，程序员可以设计出相对于无经验的用户可以操作的复杂的数据分析程序。

6.MATLAB编译器

MATLAB的灵活性和平台独立性是通过将MATLAB代码编译成设备独立的P代码，

然后在运行时解释P代码来实现的。这种方法与微软的V3相类似。不幸的是，由于

MATLAB是解释性语言，而不是编译型语言，产生的程序执行速度慢。当我们遇到执彳亍速

度慢的程序时，我们将会指出其这一特性。

MATLAB的缺点

MATLAB有两个基本的缺点。

第一，它是解释型语言，其执行速度要比编译型语言慢得多。这个问题可以通过合理

的MATLAB结构得到缓解，也可以在发行广泛使用前编译出MATLAB程序。

第二，他的费用较高。一个完全版MATLAB编译器的大小是一个C语言或Fortan语

言编译器的5至吐0倍。但MATLAB能够节省大量的时间在科技编程方面，故MATLAB在

商业编程过程中是节省成本的。尽管如此，相对于大多数考虑购买的人还是很昂贵的。幸

运的是，它有一个价格便官的学牛专用版本，对学牛来说它是学习MATLAB语言的一个重

要工具。学生版的MATLAB和完全版的MATLAB是基本一致的。随着选择和循环介绍，我

们的程序也将变得复杂，对于解决问题来说，将会变得简单。为了帮助大家避免在编程过

程中出现大量的错误，我们将向大家介绍正式的编程步骤，即自上而下的编程方法。我们

也会向大家介绍一些普通的算法开发工具即伪代码。

自上而下的编程方法简介

假设你是在工厂工作的工程师，为了解决某些问题，你要编写一个程序。你如何开始

呢？当遇到一个新问题时，我们的心里会自然而然的产生这样的想法：马上坐在计算机前，

开始编程，而不用浪费大量的时间思考我们所要解决的问题是什么？用这种不切实际的想

法来编一些非常小的程序可能会成功。但在现实中，问题可能会非常的大，程序员再用这

种方法编程将会陷入困境。对于一个大的程序来说，在编写代码之前你要通盘的思考你所

要面临的问题和解决的方法。在本节中，我们将向大家介绍正式的编程设计步骤，然后应

用这个步骤来编写本书所有的大的应用程序。对于我们所遇到一些简单的例子来说，这个

步骤好像有些画蛇添足。但是当我们解决的问题变得越来越大的时侯，这个步骤将会变得

异常重要。当我还没有毕业的时侯，一个教授喜欢说："编程很简单，因为我知道在编程的