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Java混合编程资源小结

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PuttingaJavaInterfaceonyourC,C++,orFortranCodeAbstract:ThepurposeofthisreportistodocumentsomeofthetechnicalaspectsofcreatingJavainterfacesforcodeswritteninlanguagesotherthanJava.Weoutlineaprocedurewhereoneseparatestheconstructionoftheinterfacefromtheexternalcodeswiththeintroductionofanintermediate"wrapper"class.Thisintermediateclassservestoisolateuserinterfacedetailsfromthedetailsofcallingexternalroutines.ThisintermediateclassalsofacilitatestheincorporationofexternalroutinesintoJavabasedsystemsfordistributedcomputingand/orvisualprogramming.ContentsChrisAndersonDepartmentofMathematicsUCLALosAngeles,CA915557/15/97ThesesoftwarecomponentsweredevelopedinconjunctionwiththeresearchsupportedbyAirForceOfficeofScientificResearchGrantF49620-96-I-0327andNationalScienceFoundation/ARPAGrantNSF-DMS-961584
IntroductionWhilepeoplearedebatingwhetherornotJavaisgoodforcomputationallyintensivetasks,thefactisthatC,C++andFortranaretheprimarylanguagesforthosewhodoscientific/technicalcomputing.Italsoseemsunlikelythatthissituationwillchangeinthenearfuture.Unfortunately,C,C++andFortrandonotcontain(asJavadoes)standardizedandplatformindependentconstructsforcreatinguserinterfaces,managingthreads,networking,andavarietyofothertasksassociatedwithcreating"applications".Thus,thereisinterestincreatingapplicationsinwhichtheuserinterface,orother"applicationpackaging",iswritteninJava,butthecorecomputationalcomponentiswritteninC,C++,orFortran(seeFigure1).Thepurposeofthisdocumentistodescribe,principallybymeansofanextendedexample,theprocessofcreatingaJavainterfaceforaprogramwritteninC,C++orFortran.InordertocreateapplicationswhichhavetheformindicatedinFigure1,oneneedstoknowhowtowriteJavainterfacesandhowtocallroutineswritteninC,C++andFortranfromJava.TheprocessofwritingaJavainterfaceiswelldescribedinavarietyofbooks[1][2][3][4]andwewillassumethatthereaderiscapableofwritingamodestJavainterfacewhichacceptsinputanddisplaysoutputtoauser.ThetaskofcallingroutineswritteninC,C++andFortranfromJavacomesundertheheadingofimplementingandusing"native"methods.Heretoo,otherdocuments[1][7]describetheprocessofinterfacingJavatootherlanguages.While,forcompleteness,wewilloutlinethestepsrequiredtocreateandimplementJavaclasseswithnativemethods,weassumethatthereaderhasimplementedaJavaclassthathasatleastonenativemethodprocedureinit(e.g.the"HelloWorld"exampleof[7]).Inoneaspect,thisreportisthepresentationofanextendedexampledemonstratinghowthisknowledgeofwritingJavainterfacesandimplementingnativemethodscanbecombinedtocreateaJava/"otherlanguage"application.Inadditiontoprovidingsamplesofthemechanismsfordataexchange,theexamplealsorevealsthechoiceswemade(andchoicesyouwillhavetomake)concerningthedividinglinebetweentheJavainterfaceandroutineswritteninC,C++orFortran.OurexampleconcernsthecreationofaJavainterfaceforaprogramwhichsolvestheheatequationinatwodimensionalrectangularregion.ExamplesinC++andFortranaregiven(asisreadilyseentheC++exampleisveryclosetowhatmightbecomposedinC).InthefirstsectionweoutlinetheprocessthatwefollowforcreatingapplicationsofthetypedescribedbyFigure1.Inthesecondsectionwepresenttheexamplewhichwillformthebasisofourdiscussion,andinthethirdandfourthsectionswedetailtheconstructionoftheJavaclasseswhichformtheprimarycomponentsoftheapplication.
TheprocessofcreatingaJavainterfacetoC,C++andFortranroutinesTheprocessthatweuseforcreatingJavainterfacesconsistsofthethreestepsindicatedinfigure2.Anoticeablefeatureoftheprocessisthatweutilizethreesteps,ratherthantwo.Onemaywonderabouttheneedfortheintermediatestep;thatofwritinganintermediateclassthat``wraps''theC,C++orFortrancode.Originallywedidn'thavethreesteps,butadoptedthispracticeforseveralreasons:Itfacilitatedhavingtheexternalcoderunasaseparatethread.Ifoneisrunningacomputationallyintensivetask,thenthisallowsthetasktobeexecutedwithout``freezing''theinterface.
Byusingthisintermediateclasswehaveisolatedthatcomponentoftheapplicationwhichcontainsinter-languagecalls.Sincetheinter-languagecallingprocedureforJavaisevolving,thisallowsustoaccommodateanychangesintheinter-languageproceduresmoreeasily.Additionally,bynotembeddingthiscodewithinauserinterface,wealsoallowtheuserinterfacetochangeindependently(thisisimportantbecausetheJavauserinterfaceclassesareevolvingaswell).
Lastly,andnolessimportantly,thisclassprovidesanencapsulationoftheexternalroutineswhichfacilitatestheirincorporationinavisualprogrammingsystemorasoftwareinfrastructurewhichsupportsdistributedcomputing.

Theexampleprogramwrittenin"another"language.ThestartingpointfortheprocessofwritingaJavainterfaceistohaveaprogramoraselectedsetofcodecomponentsthatonewishestowriteinterfacesfor.Ratherthandiscusstheprocessofwritinginterfacesinanabstractway,wediscusstheprocessofwritinginterfacesforaspecificexample.Theexampleprogramisonethatcomputestheevolutionofthetemperatureofarectangularplate.Themaindriverroutineisgivenbelow(aswellasinthefiletempCalc.cpp);theincludefileforthefunctionswhichthemainroutinecallsaregivenintempCalcRoutines.handthesourcefortheseroutinesisgivenintempCalcRoutines.cpp.Inthefirstpartofthemainroutine,theproblemandrunparametersareset,memoryisallocatedandthetemperaturedistributionisinitialized.Atimesteppingloopisthenexecuted.Inthisloop,thetemperatureoftheplateisevolvedintimeincrementsofsizedtbycallingtheroutineevolveTemperature(...)andatsomepredeterminednumberoftimestepsthetemperaturedistributionisoutput.(InthiscasewrittentoafiletempOut.dat).Eventhoughthetemperaturevaluesareassociatedwithatwo-dimensionalsetofnodescoveringtheplate,weallocateandpassone-dimensionalarraysofvalues.Thiswasdonebecausethestandardmethodforexchangingdatawithotherlanguagesisthroughone-dimensionalarrays;Javaisnoexception.Usingone-dimensionalsetsofdatavaluesdoesnotprecludeusingatwo-dimensionalarraystructuretoaccessthedata.Theroutinescreate2dArrayStructure(...)anddestroy2dArrayStructure(...)intempCalcRoutines.cppdemonstratehowonecancreateatwo-dimensionalarraystructurewhichaccessthedataallocatedasaonedimensionalarray.
#include<iostream.h>#include<fstream.h>#include"tempCalcRoutines.h"voidmain(){////SetProblemparameters//doublediffusivity=0.1;doublea=0.0;doubleb=1.0;doublec=0.0;doubled=1.0;////SetRuntimeparameters//longm=10;longn=20;longnSteps=100;longnOut=10;doubledt=0.01;////Allocatespaceforsolutionandworkarrays//double*Tarray=newdouble[m*n];double*workArray=newdouble[m*n];////Openoutputfile//ofstreamFout("tempOut.dat");initializeTemperature(Tarray,m,n,a,b,c,d);doubletime=0.0;inti;intj;for(i=1;i<=nSteps;i++){evolveTemperature(Tarray,m,n,a,b,c,d,dt,diffusivity,workArray);time=time+dt;if((i%nOut)==0){cout<<"Step"<<i<<endl;//printoutsteptoscreenFout<<m<<""<<n<<endl;//outputtofiletempOut.dat...Fout<<time<<endl;for(j=0;j<m*n;j++){Fout<<Tarray[j]<<endl;}}}delete[]Tarray;delete[]workArray;}Thisprogramistypicalofmanycomputationallyintensiveapplications;dataisallocated,parametersandvaluesareinitialized,andthenatimesteppingloopisexecuted.Asthecalculationproceedsdataisoutputperiodically.TheFortranversionofthisprogramisgivenintempCalc.fandthesupportingroutinesaregivenintempCalcRoutines.f.OnemaynoticethattheC++programisnearlyidenticaltotheFortranprogramanddoesnotuseanyoftheobjectorientedfeaturesofC++(i.e.itdoesnotutilizeclasses).Thiswasdoneintentionallysothatthecodewouldserveasanexampleofcodeswhicharelikelytobeused(and/orwritten)bythemajorityofthoseinvolvedinscientific/technicalcomputation.
TheJavaclassthatencapsulatestheC,C++orFortrancodescomponents.ThesecondstepintheprocessofcreatinganinterfaceistocreateaJavawrapperclassthatencapsulatestheC,C++orFortrancodecomponents.ItisinthisclassthattheconnectionbetweentheexternalroutinesandthecorrespondingJavaroutinesismade.Thisclassisalsoresponsiblefor"loading"theexternalroutines.Essentially,thisclassreplacesthemain()routine.Inthisregardtheclassallocatestherequiredarrays,containstheparametersasdatamembersandalsocontainsthemethods(declarednative)whichareinvokedbythemain()driverroutine(theinitializeTemperatureandevolveTemperatureroutines).Tofacilitatetheexecutionoftheprogramasaseparatethread,thisclassimplementstheRunnableinterface(itimplementsarun()method).Inthisrun()method,wehavechangedtheoutputprocesstobeonewhichdisplaysacolorcontourplotofthedata,ratherthanwritetheoutputtoafile.TherequisiteJavaclassesarecontainedinthefilesColorContourPlot.java,ColorContourCanvas.javaandContourResolutionDialog.java.Lastlythisroutinealsoincludesamainroutineofit'sownfortestingpurposes.ThecompletecodeisgiveninTempCalcJava.java.Sincethisroutinehasnativemethods,onemustcreatethedynamicallylinkedlibrary(DLL)orsharedlibrarythatcontainstheirimplementations.Asoutlinedinthediscussionsonimplementingnativemethods[1][7],thisisamulti-stepprocess:TheclassTempCalcJava.javaiscompiled.Eventhoughthenativemethodsarenotimplemented,youmustcompiletheJavaclasscontainingthenativemethodsbeforeperformingthenextstep.
ThecommandjavahisappliedtoTempCalcJava.class.Thismeansexecuting"javah-jniTempCalcJava".TheresultofthiscommandisthecreationofthefileTempCalcJava.h.SinceweareusingthenativeinterfacespecificationofJava1.1,thejavahcommandmustbetheonedistributedwiththeJDK1.1.
ThefunctionscontainedinTempCalcJava.hare"implemented".InthisregardourtaskconsistsofaccessingthedatacontainedwithintheJavaarraysandpassingittothecorrespondingC++(orFortranroutines).TheimplementationoftheseroutinesisgiveninTempCalcJava.cpp.(NotethatonecanselecttheFortranimplementationbydefining__FORTRAN_BUILD__inthecompilationprocess.)
TheroutinesinTempCalcJava.cppalongwiththoseintempCalcRoutines.cpparecompiledandadynamicallylinkedlibrary(orasharedlibrary)iscreated.Thenameofthislibrarymustcoincidewiththenameofthefile(withoutthe.dllor.soextension)whichoccursinSystem.loadorSystem.loadLibrarycommandwithinthestaticinitializerfortheclass.(ForsomenotesonthecompilationprocessseeNativeMethodCompilationNotes.)
See"NativeMethodImplementationProcess"foradiagramofthesesteps.Atthispoint,ifthenativemethodimplementationprocessissuccessful,oneshouldbeabletoruna"commandline"versionoftheprogrambyexecutingthemainroutineoftheclassi.e.justexecute"javaTempCalcJava".Problemswhichoccuratthispointareoftencausedbyincorrect,ornon-specification,ofthepathwhichissearchedforthelibrarycontainingthenativemethodimplementation.OnPC/WindowsplatformsthePATHvariablemustincludethedirectorycontainingthenativemethodimplementationdll.OnUNIXmachinesrunningsolaristheLD_LIBRARY_PATHvariablemustincludethedirectorycontainingthenativemethodimplementationsharedlibrary.
TheJavaInterfaceThethirdstepinwritingtheinterfaceistowritetheJavaclassthatimplementstheinterface.MinimallythismeanscreatingaJavaapplicationthatpossessesprogramcontrolbuttonsandfieldsfordatainput.Theinterfaceisdisplayedbelow,andtheassociatedJavacodeiscontainedwithinTemperatureApp.java.ThisuserinterfacewasconstructedusingtoolsthatgenerateJava1.0.2.However,sinceourimplementationofnativemethodsisJava1.1based,aftertheinitialconstruction,wecompiledandworkedwiththiscodeusingtheJava1.1compiler.IntheJava1.1compilationsteponemustspecifytheflag"-deprication"andputupwithallthewarningsthataregenerated.HopefullytheinterfaceconstructiontoolswillsupportJava1.1soonandthesenuisanceswilldisappear.InlookingovertheJavacode,oneshouldtakenotethatthecomputationallyintensivepartoftheapplicationisdoneasaseparatethread[6].Specifically,withinthecodewhichgetsexecutedwhentheRunbuttonishit(thecodefragmentisgivenbelow)wecreatethreadsfortheseparatecomponentsoftheapplication---onethreadforthecalculationcomponentandonethreadforthecolorcontourplot.Thecalculationcomponentthreadisgivenalowerpriority,sothatonmachineswhoseimplementationoftheJavavirtualmachinedoesn'ttime-sliceamongequalprioritythreads,thecomputationallyintensivecomponentwillnotcausetheuserinterfaceto"freeze".voidRunButton_Clicked(Eventevent){***////Setupandstartthethreadsforthecontourplotandthe//calculation//Threadcurrent=Thread.currentThread();//capturecurrentthreadThreadcontourThread=newThread(temperatureRun.contourPlot);contourThread.start();TempRunThread=newThread(temperatureRun);TempRunThread.setPriority(current.getPriority()-1);TempRunThread.start();}Thecolorcontourplotthatresultsfromtheexecutionoftheprogramisgivenbelow//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////Java/FortranInterfaceThistutorialgivesanexampleofhowtointerfaceFortranandJava.ItisintendedtosupplementtheexamplegiveninJava/FortranInterfacetipsandit'sagoodideatoreadthatsitefirst.TheexamplewasdevelopedonSunSolarisusingSunWorkshop5.0C++andFortrancompilersandSunJDK1.2.Becausetheexampleisnolongerfullyportable,itmaynotworkonyoursystemandIdon'tknowenoughaboutothersystemstoreallyhelpyou.So,ifyoudomanagetogetthingsrunningonothersystemsthenpleasesendinyourtipsandmakefilesforthebenefitofotherusers.Whydoit?Javaprovidesobject-orientedprogramming,easyvisualisationandtrueportability.Fortranhasnoneofthesethingsbutdoesofferhighlyoptimisedcompilers(withtheoptionofparallelisation),excellentnumericallibraries,simplicity,mathssupport(e.g.complexnumbersandmulti-dimensionalarrays)andmassesoflegacycodeallofwhichmakeitexcellentfornumbercrunching.AlthoughonemightliketomoveovertopureJava,theperformanceadvantagesofFortranortheeffortofconvertinglegacycodeoftenenforcesadualapproachwithaninterfacebetweenthetwolanguages.IntroductionThistutorialwillworkthroughanexamplewhichsetssomevariablesinJava,changestheminFortranandshowstheeffectinJava.TheJavaprogrammustcalltheFortransubroutineviaaC++wrapper(asexplainedinJava/FortranInterfacetips)becauseJavacanonlytalktoCorC++.Thevariablesareintegers,doubles,booleansandstrings,oneofeachwiththesuffix"_A"andonewiththesuffix"_B".EachvariablewillbesetinJavaandresetinFortran.However,onlythechangesinthe"_A"variablesarepassedthroughtoJavaviatheC++wrapper.Inadditiontwo2-Darrays(adoubleprecisionarrayandacomplexdoubleprecisionarray)arepassedtoFortran.ThesearraysareoverwrittenintheFortransubroutine.BecauseJavadoesnotsupportmulti-dimensionalarrays,a2-Darrayofsize(mx,my)isreferencedasa1-Darreyofsize(mx*my).Inaddition,Javadoesnotsupportcomplexnumberssoa2-Dcomplexarrayofsize(mx,my)isreferencedasa1-Darrayofsize(2*mx*my).TheJavaprogramTheJavaprograminitialisesthevariablesandechoesthemtothescreen,thencallstheFortransubroutinethroughitsC++wrapperandechoestheupdatedvariablevalues.Inthelinepublicnativevoidcppsub(intint_A,intint_B,doubledouble_A,doubledouble_B,booleanbool_A,booleanbool_B,intmx,intmy,double[]doubleArray,double[]complexArray,Stringstring_A,Stringstring_B);wedeclareanativeroutine"cppsub"(ourC++wrapper).Inthelinestatic{System.loadLibrary("JniDemo");}weloadinthedynamiclibrary"libJniDemo.so".TheJavacodeiscompiledby"javacJniDemo.java"andisfoundhere:JniDemo.java.Noticehowthe1-DJavaarraysareunpackedtoaccessthe2-DFortranarrays.JavaincludefileWecanautomaticallygenerateaJavaincludefileforthenativeroutine"cppsub"fromJniDemo.classbytyping"javah-jniJniDemo".Theincludefileisfoundhere:JniDemo.h.andgivesusthedeclarationofthesubroutine"Java_JniDemo_cppsub"fortheC++wrapper.AlltheJavaintegers,doublesetc.havebeenpassedasC++typesjint,jdoubleetc.specifiedin"jni.h".TheC++wrapperTheC++wrapperistheheartoftheinterfaceandmustdomorethansimplypassitsparameterstoFortran.ThelinkbetweenFortranandC++isunfortunatelynotstandardised.InformationontheSolarisinterfaceisfoundhere:Fortran/CInterface.Thelineextern"C"voidf90sub_(int*int_A,int*int_B,double*double_A,double*double_B,unsignedchar*bool_A,unsignedchar*bool_B,int*mx,int*my,double*doubleArray,double*complexArray,constchar*str_A,constchar*str_B,int*str_A_len,int*str_B_len);declarestheexternallycompiledFortransubroutine"f90sub"whichgetsanunderscoreaddedtoitsname.Theroutineiscalledwith:f90sub_(&int_A,&int_B,&double_A,&double_B,&bool_A,&bool_B,&mx,&my,daPtr,caPtr,str_A,str_B,&str_A_len,&str_B_len);Allthevariablesarepassedbyreference.NotethatthejbooleansmustbepassedtoFortranastypeunsignedchar.Letusfirstlookatthescalarvariables(jint,jdouble,jboolean).ThesecansimplybepassedbyreferencetoFortran.OnreturnfromtheFortransubroutine,thecorrespondingJavavariablesendingin"_A"areupdatedby:jclasscls=env->GetObjectClass(obj);
jfieldIDfid;

....

fid=env->GetFieldID(cls,"int_A","I");
if(fid==0){
return;
}
env->SetIntField(obj,fid,int_A);

fid=env->GetFieldID(cls,"double_A","D");
if(fid==0){
return;
}
env->SetDoubleField(obj,fid,double_A);

fid=env->GetFieldID(cls,"bool_A","Z");
if(fid==0){
return;
}
env->SetIntField(obj,fid,bool_A);wherewedirectlyoverwritethevariables"int_A","double_A"and"bool_A"inthecallingobject"obj".Forthearrays,wecreatepointerstothosearraysbycallingaJNIroutine"GetDoubleArrayElements"andpassthosetotheFortransubroutine.BeforeleavingtheC++wrapperwemustcall"ReleaseDoubleArrayElements"incaseJavahadtomakeacopyofthearray(seeJavaNativeInterfacetutorial).jdouble*caPtr=env->GetDoubleArrayElements(complexArray,0);
jdouble*daPtr=env->GetDoubleArrayElements(doubleArray,0);

...

env->ReleaseDoubleArrayElements(complexArray,caPtr,0);
env->ReleaseDoubleArrayElements(doubleArray,daPtr,0);Passingstringsisslightlymorecomplicated.Wefirstdefinepointers"str_A"and"str_B"andgetthelengthsofthestringsusing"GetStringUTFChars"and"GetStringLength"andpassthosetoFortran:jstringjstr;
intstr_A_len,str_B_len;

constchar*str_A=env->GetStringUTFChars(string_A,0);
str_A_len=env->GetStringLength(string_A);
constchar*str_B=env->GetStringUTFChars(string_B,0);
str_B_len=env->GetStringLength(string_B);Nextwemakeacopyofthestring"str_A"toensureitisonly"str_A_len"characterslong:charbuf[128]="";
strncat(buf,str_A,str_A_len);Nowwecreatethejstring"jstr"usingtheJNImethod"NewStringUTF"andusethattooverwritetheJavastring"string_A"inthecallingprogram:fid=env->GetFieldID(cls,"string_A","Ljava/lang/String;");
if(fid==0){
return;
}
jstr=env->NewStringUTF(buf);
env->SetObjectField(obj,fid,jstr);Finally,wemustreleasethestringelements:env->ReleaseStringUTFChars(string_A,str_A);
env->ReleaseStringUTFChars(string_B,str_B);HereistheC++wrappercode:JniDemo.cppInSolaris,theC++wrapperiscompiledtocreatethedynamiclibrary"JniDemo.so"somethinglike:CC-G-I/usr/java/include-I/usr/java/include/solaris-oJniDemo.soJniDemo.cppTheFortransubroutineTheFortransubroutinefirstprintsoutallthevariablespassedtoit,thenoverwritesthemallandfinallyprintsoutthevariablesagain.Notethatbooleans(Fortranlogicals)mustbeconvertedfromtheunsignedcharsthatwerepassedfromtheC++wrapperwiththelines:bool_A=(cbool_A.eq.char(1))
bool_B=(cbool_B.eq.char(1))Attheend,theFortranlogicalsmustbeconvertedbacktounsignedcharacterswiththelines:cbool_A=char(0)
cbool_B=char(0)
if(bool_A)cbool_A=char(1)
if(bool_B)cbool_B=char(1)ThepassingsofcharacterstringsbetweenC++andFortranisnotstandardisedsowehaveusedcharacterarraysandpassedaseparateintegerwiththestringlength.ThearraysareindexedinthenormalFortranfashion.Thefortransubroutineisfoundhere:JniDemo_fortran.fInSolaris,wecompilethefortransubroutineandlinkintheC++wrapperlikethis:f90-lF77_mt-lM77-lfsu-lf77compat-G-L/usr/java/jre/lib/sparc-ljava-I/usr/java/include-I/usr/java/include/solaris-olibJniDemo.soJniDemo.soJniDemo_fortran.fThemakefileHereisthemakefileforSunSolaris:makefile.Itishopefullyeasytoadapttoyoursystem.Notethatfileswiththesuffix".so"aredynamiclibraries(equivalentto".DLL"filesinWindows).The"-G"compilerflagsignalscreationofadynamiclibrary.The"-o"flagnamestheoutputfile.The"-I"flagsignalsincludefiles.The"-L"flagsignalsthedirectorywherelibrariestobelinkedtoarekeptandthe"-l"flagnamesindividuallibraries(thenamesareexpandede.g.-ljavaindicatesfilelibjava.so).Here,dynamiclibrariesareusedthroughoutratherthanobjectfiles.ThefinallinkingstepmustbedonewiththeFortranf90compilersothedynamiclibrary"libJniDemo.so"iscreatedbylinkingthelibraries"JniDemo.so"andJniDemo_fortran.so"together.OutputoftheprogramCompiletheprogramusing"make"andrunitusing"javaJniDemo".Youshouldgettheoutputshownhere:Outputof"javaJniDemo".Notethattheprintstatementsmaybejumbledasyoushouldn'treallymixJavaandnativeinput/output.Ihopeyougotittowork.Nowtryadaptingittosuityourneeds.Ifthere'sanythingthathasn'tbeencoveredthenletmeknowattheaddressbelow.Goodluck!NotesThereseemstobeaproblem(usingSun/Solaris/Workshop)whenusinge.g.REAL(8)andCOMPLEX(16)inFortran90insteadofREAL*8andCOMPLEX*16.Igetthemessage:

FATALERRORinnativemethod:Trytounpinanobjectthatisnotpinned

Idon'tknowwhythisisandtheworkaroundistojustusetheREAL*8notation.Pleaseemailmeifyouknowwhat'sgoingon...//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

WhynotsticktoJavaorC/C++?

FeaturesofPerlandPythoncomparedwithJava,C/C++andFortran:

	shorterprograms
	muchfasterdevelopment
	novariabledeclarations, butlotsofconsitencychecksatruntime
	lotsofgluingtools
	lotsoftextprocessingtools
	GUIsaresimpler/shorter
	lotsofWebprogrammingtools

Thepopularityofscriptingisgrowingfast!

Scriptingisontherise

	70s/80s:Unixshell,jobcontrollanguages(primitive,crypticprogramming)
	90s:DevelopmentofPerl,Python,Ruby,Tcl++
	Y2K:Scriptinglanguagesarestableandpowerfulonallmajorplatforms
	Nextdecade:explosiveinterest???
	Scriptingsupportssoftwarereuse
	ScriptingsimplifiesGUIprogramming
	Scriptsarefastenoughontoday'scomputers
	PythonsupportsbothshortscriptsandJava/C++-likesystems

GUI:PythonvsC

	Case:makeawindowonthescreenwiththetext'HelloWorld'
	C+X11:176linesofuglycode
	Python+Tk:6linesofreadablecode #!/usr/bin/envpython fromTkinterimport* root=Tk() Label(root,text='Hello,World!', foreground="white",background="black").pack() root.mainloop()
	JavaandC++codesarelongerthanPython+Tk

TherelationtoOOP

·	Object-orientedprogrammingcanalsobeusedtoparameterizetypes
·	IntroducebaseclassAandarangeofsubclasses,allwitha(virtual)printfunction
·	LetdebugworkwithvarasanAreference
·	NowdebugworksforallsubclassesofA
·	Advantage:completecontrolofthelegalvariabletypesthatdebugareallowedtoprint(maybeimportantinbigsystemstoensurethatafunctioncanallowmaketransactionswithcertainobjects)
·	Disadvantage:muchmorework,muchmorecode,lessreuseofdebuginnewoccasions

WhentouseC,C++,Java,Fortran

	Doestheapplicationimplementcomplicatedalgorithmsanddatastructures?
	Doestheapplicationmanipulatelargedatasetssothatexecutionspeediscritical?
	Aretheapplication'sfunctionswell-definedandchangingslowly?
	Willstrongtypingbeanadvantage,e.g.,inlargedevelopmentteams?

Personalapplicationsofscripting

	Automatemanualinteractionwiththecomputer
	Customizeyourownworkingenvironmentandbecomemoreefficient
	Havemorefun
	Increasethereliabilityofyourwork (whatyoudidisdocumentedinthescript,visualizationscanbeautomaticallytaggedwithinputdata)
	Scripts(usually)runonUnix,Windows,Macandmanyhand-helddevices(i.e.scriptsarecross-platform)
	YougetthepowerofUnixalsoinnon-Unixenvironments

Python'sadvantagesoverPerl

	Pythoniseasiertolearnbecauseofitscleansyntaxandsimple/clearconcepts
	PythonsupportsOOinamucheasierwaythanPerl
	GUIprogramminginPythoniseasier (becauseoftheOOfeatures)
	DocumentingPythoniseasierbecauseofdocstringsandmorereadablecode
	ComplicateddatastructuresareeasiertoworkwithinPython
	PythonissimplertointegratewithC++andFortran
	PythoncanbeseamlesslyintegratedwithJava

Perl'sadvantagesoverPython

	Perlismorewidespread
	Perlhasmoreadditionalmodules
	Perlisfaster
	Perlenablesmanydifferentsolutionstothesameproblem
	Perlprogrammingismorefun(?)andmoreintellectuallychallenging(?)

Pythonistheveryhigh-levelJava,
Perlisverythehigh-levelC?

NumericalPython(NumPy)

	NumPyenablesefficientnumericalcomputinginPython
	NumPyisaPython/Cpackagewhichoffersefficientarrays(contiguousstorage)andmathematicaloperationsinC
	OldNumericmodule:fromNumericimport*
	NewNumarraymodule: fromnumarrayimport* NumPycontainsothermodulesaswell

Pythonandnumericalcomputing

	Filla2DNumPyarraywithfunctionvalues: n=2000 a=zeros((n,n),Float) xcoor=arange(0,1,1/float(n)) ycoor=arange(0,1,1/float(n)) foriinrange(n): forjinrange(n): a[i,j]=f(xcoor,ycoor[j])
	Fortran/C/C++version:(normalized)time1.0
	Pythonversion:time75
	NumPyvectorizedevaluationoff:time3

Conclusions

	Pythonloopsoverarraysareextremelyslow
	NumPymaybesufficient
	However,NumPyvectorizationmaybeinconvenient -plainloopsinFortran/C/C++aremucheasier!
	WriteadministeringcodeinPython
	Identifybottlenecks(viaprofiling)
	MigrateslowPythoncodetoFortran,C,orC++

ThenatureofPythonvs.C

APythonvariablecanholddifferentobjects:

d=3.2#dholdsafloat

d='txt'#dholdsastring

d=Button(frame,text='push')#instanceofclassButton

InC,C++andFortran,avariableisdeclaredofaspecifictype:

doubled;d=4.2;

d="somestring";/*illegal,compilererror*/

ThisdifferencemakesitquitecomplicatedtocallC,C++orFortranfromPython

CallingCfromPython

	SupposewehaveaCfunctionexterndoublehw1(doubler1,doubler2);
	WewanttocallthisfromPythonas fromhwimporthw1 r1=1.2;r2=-1.2 s=hw1(r1,r2)
	ThePythonvariablesr1andr2holdnumbers,weneedtoextracttheseintheCcode,converttodoublevariables,andthencallhw1
	Thisisdoneinwrappercode

Wrappercode

BetweenPythonandhw1weneedwrappercode:

staticPyObject*_wrap_hw1(PyObject*self,PyObject*args){

PyObject*resultobj;

doublearg1;

doublearg2;

doubleresult;

if(!PyArg_ParseTuple(args,(char*)"dd:hw1",&arg1,&arg2)){

returnNULL;/*wrongargumentsprovided*/

result=(double)hw1(arg1,arg2);

resultobj=PyFloat_FromDouble(result);

returnresultobj;

Python+Matlab=true

APythonmodule,pymat,enablescommunicationwithMatlab:

fromNumericimport*

importpymat

x=arrayrange(0,4*math.pi,0.1)

m=pymat.open()

#cansendNumPyarraystoMatlab:

pymat.put(m,'x',x);

pymat.eval(m,'y=sin(x)')

pymat.eval(m,'plot(x,y)')

#getanewNumPyarrayback:

y=pymat.get(m,'y')

ComparisonwithMatlab

	ThedemonstratedfunctionalitycanbecodedinMatlabaswell
	WhyPython+F77?
	Wecandefineourowninterfaceinamuchmorepowerfullanguage(Python)thanMatlab
	WecanmuchmoreeasilytransferdatatoandfromorownF77orCorC++libraries
	Wecanuseanyappropriatevisualizationtool
	And,ofcourse,wecancallupMatlabifwewant
	Python+F77givestailoredinterfacesandmaximumflexibility

DisadvantagesofFortran77

	Thebasicvariablestypesareprimitive
	NostructorclassconstructinF77
	Nodynamicmemoryallocation
	Veryprimitivelanguagefortextprocessing,listsandmorecomplicateddatastructures
	F77codesaredifficulttoextend,maintainandre-use
	F90/F95:extensionofF77withclasses (butnotvirtualfunctions,templatesetc.)
	TheefficiencyofF90/F95isstillproblematic,andF77programmersmoveveryslowlytoF90/F95

AdvantagesofFortran77

	F77isaverysimplelanguage
	F77iseasytolearn
	F77wasmadeforcomputingmathematicalformulasandoperatingefficientlyonplainarrays
	F77isstill(andwillforeverbe?)thedominatinglanguagefornumericalcomputing
	LotsofwelltestedandefficientF77librariesexist
	Compilershave50yearsofexperiencewithoptimizingF77loopsoverarrays
	Result:F77ishardtobeatwhenitcomestoarrayoperations

Myopinion

	UseF77fortime-criticalloops(arrayoperations)
	MaketherestoftheprograminPython,C++,JavaorF95
	PythonandF77isaneasy-to-usepair!
	Note:integrationofF77withC++orJavaisnotalwaysstraightforward

//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

AboutthisPage

[i]AprogrammercanbesignificantlymoreproductiveinPythonthaninJava.Howmuchmoreproductive?Themostwidelyacceptedestimateis5-10times.Onthebasisofmyownpersonalexperiencewiththetwolanguages,Iagreewiththisestimate.ManagerswhoareconsideringaddingPythontotheirorganization'slistofapproveddevelopmenttools,however,cannotaffordtoacceptsuchreportsuncritically.Theyneedevidence,andsomeunderstandingofwhyprogrammersaremakingsuchclaims.Thispageisforthosemanagers.Onthispage,Ipresentalistofside-by-sidecomparisonsoffeaturesofJavaandPython.Ifyoulookatthesecomparisons,youcanseewhyPythoncanbewrittenmuchmorequickly,andmaintainedmuchmoreeasily,thanJava.Thelistisnotlong--itismeanttoberepresentative,notexhaustive.Thispagelooksonlyatprogrammerproductivity,anddoesnotattempttocompareJavaandPythononanyotherbasis.Thereis,however,onerelatedtopicthatisvirtuallyimpossibletoavoid.Pythonisadynamically-typedlanguage,andthisfeatureisanimportantreasonwhyprogrammerscanbemoreproductivewithPython;theydon'thavetodealwiththeoverheadofJava'sstatictyping.SothedebatesaboutJava/Pythonproductivityinevitablyturnintodebatesaboutthecomparativeadvantagesanddrawbacksofstatictypingversusdynamictypinga€”orstrongtypingversusweaktypinga€”inprogramminglanguages.Iwillnotdiscussthatissuehere,otherthantonotethatinthelastfiveyearsanumberofinfluentialvoicesintheprogrammingcommunityhavebeenexpressingseriousdoubtsaboutthesupposedadvantagesofstatictyping.Forthosewhowishtopursuethematter,StrongversusWeakTyping:AConversationwithGuidovanRossum,PartVisagoodplacetostart.SeealsoBruceEckel'sweblogdiscussionStrongTypingvs.StrongTestingandRobertC.Martin'sweblogdiscussionAreDynamicLanguagesGoingtoReplaceStaticLanguages?.Forbackground,seeoneofthepapersthatstarteditallin1998—Scripting:HigherLevelProgrammingforthe21stCenturybyJohnOusterhout.SeveralofthesediscussionscontainvaluablecomparisonsofJavaandPython.Forotherlanguagecomparisons,seethePythonlanguagecomparisonspageatwww.python.org,andthePythonComparedToJavapageatPythonforJavaProgrammers.Finally,itisimportanttonotethatassertingthataprogrammercanbemoreproductiveinPythonthaninJava,isnotthesameasassertingthatoneoughtalwaystousePythonandnevertouseJava.Programminglanguagesaretools,anddifferenttoolsareappropriatefordifferentjobs.Itisapoorworkmanwhosetoolboxcontainsonlyahammer(nomatterhowbigitis!),anditisapoorprogrammer(orsoftwaredevelopmentorganization)whosedevelopmenttoolkitcontainsonlyoneprogramminglanguage.OurtoolboxesshouldcontainbothPythonandJava,sothatinanygivensituationwehavetheoptionofchoosingthebesttoolforthejob.SoourclaimisnotthatPythonistheonlyprogramminglanguagethatyou'lleverneed—onlythatthenumberofjobsforwhichPythonisthebesttoolismuchlargerthanisgenerallyrecognized.

Javavs.PythonProductivity-anOverview

TherearethreemainlanguagecharacteristicsthatmakeprogrammersmoreproductivewithPythonthanwithJava.

Java	Python
staticallytypedInJava,allvariablenames(alongwiththeirtypes)mustbeexplicitlydeclared.Attemptingtoassignanobjectofthewrongtypetoavariablenametriggersatypeexception.That'swhatitmeanstosaythatJavaisastaticallytypedlanguage.Javacontainerobjects(e.g.VectorandArrayList)holdobjectsofthegenerictypeObject,butcannotholdprimitivessuchasint.TostoreanintinaVector,youmustfirstconverttheinttoanInteger.Whenyouretrieveanobjectfromacontainer,itdoesn'trememberitstype,andmustbeexplicitlycasttothedesiredtype.	dynamicallytypedInPython,youneverdeclareanything.Anassignmentstatementbindsanametoanobject,andtheobjectcanbeofanytype.Ifanameisassignedtoanobjectofonetype,itmaylaterbeassignedtoanobjectofadifferenttype.That'swhatitmeanstosaythatPythonisadynamicallytypedlanguage.Pythoncontainerobjects(e.g.listsanddictionaries)canholdobjectsofanytype,includingnumbersandlists.Whenyouretrieveanobjectfromacontainer,itremembersitstype,sonocastingisrequired.Formoreinformationonstaticvs.dynamictyping,seetheappendix.
verbose"aboundinginwords;usingorcontainingmorewordsthanarenecessary"	concise(akaterse)"expressingmuchinafewwords.Impliesclean-cutbrevity,attainedbyexcisionofthesuperfluous"
notcompact	compactInTheNewHacker'sDictionary,EricS.Raymondgivesthefollowingdefinitionfor"compact":Compactadj.Ofadesign,describesthevaluablepropertythatitcanallbeapprehendedatonceinone'shead.Thisgenerallymeansthethingcreatedfromthedesigncanbeusedwithgreaterfacilityandfewererrorsthananequivalenttoolthatisnotcompact.

ThereasonforthisisthatJava,virtuallyaloneamongobject-orientedprogramminglanguages,usescheckedexceptions—exceptionsthatmustbecaughtorthrownbyeverymethodinwhichtheymightappear,orthecodewillfailtocompile.Recently(asofJune2003)thereseemstobeanincreasingamountofunhappinesswithJava'suseofcheckedexceptions.SeeBruceEckel's"DoesJavaneedCheckedExceptions?"andRonWaldhoff's"Java'scheckedexceptionswereamistake".Aschromatic,theTechnicalEditoroftheO'ReillyNetwork,putit:

Iliketheideaofcheckedexceptionsinsomesituations,butforcingeverymethodtodealwith(catchingorthrowing)allexceptionsthatitschildcallsormaycallcanbetedious.I'dratherbeabletoignoreanexceptionandletitpropagateupwards.Sometimes,I'drathernotworryaboutexceptionsatall.

Example

InWhyPython?EricS.Raymondnotesthat:Python...iscompact--youcanholditsentirefeatureset(andatleastaconceptindexofitslibraries)inyourhead.InWhyILovePythonBruceEckelnotesthatJavaisnotcompact.IcanremembermanyPythonidiomsbecausethey'resimpler.That'sonemorereasonIprogramfaster[inPython].IstillhavetolookuphowtoopenafileeverytimeIdoitinJava.Infact,mostthingsinJavarequiremetolooksomethingup.

Example

Java'sstring-handlingcapabilitiesaresurprisinglyweak.(ButtheyhaveimprovedconsiderablywiththeadditionofthesplitmethodtotheStringclassinJava1.4.)Example[/b]CodetoaddaninttoaVector,andthenretrieveit.Thisexampleillustratesboththeverbosityandnon-compactnessofJava,whencomparedtoPython.InJava,anewIntegerobjectmustbecreatedandinitializedfromtheintbeforeitcanbeaddedtotheVector.Inordertoretrievethevalue,thememberoftheVectormustbecastbacktoanInteger,andthenconvertedbacktoanint.InPython,noneoftheseconversionsarenecessary.

Java

Python

publicVectoraList=newVector;

publicintaNumber=5;

publicintanotherNumber;

aList.addElement(newInteger(aNumber));

anotherNumber=((Integer)aList.getElement(0)).intValue();

aList=[]

aNumber=5

aList.append(aNumber)

anotherNumber=aList[0]

Inparticular,thisexampleillustratestheclumsinessofcontainerobjectsinJava,whichrequirecastinganobjectwheneveritisextractedfromacontainer.ItisacommonpracticeamongJavaprogrammerstoovercomethisclumsinessbywritingapplication-specificcontainerobjectstowrapJava'sgenericcontainers.Youmight,forexample,haveanEmployeesclasstowrapavectorofEmployeeobjects.Theget()methodoftheEmployeesobjectwouldretrievetheappropriatememberoftheVector,andcastitbacktoanEmployeeobjectbeforereturningit.ThisisactuallyagoodpracticeinJava.Butithastheeffectofincreasingthenumberofclassesintheapplication--classesthattheprogrammermustwrite--and(becauseeachJavaclassmustexistinitsownfile)itincreasesthenumberofJavafilesthattheprogrammermustmanage.Noneofthis,ofcourse,isnecessaryinPython.TheburdenonJavaprogrammerswillbeeasedsomewhatinJava1.5withtheintroductionofgenericsandboxingconversions,alsoknowasautoboxing.

Example

Verbosityisnotjustamatterofincreasingthenumberofcharactersthatmustbetyped--itisalsoamatterofincreasingthenumberofplaceswheremistakescanbemade.TheJavacodeonthelefthas5controlcharacters:(){};wherethecorrespondingPythoncodehasonlyonecontrolcharacter,thecolon.(Ortwo,ifyoucountindentation.Seebelow.)

Java

Python

if(a>b)

a=b;

b=c;

ifa>b:

a=b

b=c

Omittingorduplicatingsuchcharactersiseasytodoaccidentally,andconstitutesasevereerrorinthecode.Inmypersonalestimate,Ispend5timesasmuchtimefixingsucherrorsinJavaasIdoinPython.Itreallycutsintoyourproductivity--andyourcreativeenergy--whenyouspendthatmuchofyourtimejusttryingtosatisfythecompiler.Technically,PythonhasanothercontrolcharacterthatJavadoesnota€”indentation.ButtherequirementforcorrectindentationisthesameinJavaasitisinPython,becauseinbothlanguagescorrectindentationisapracticalrequirementforhuman-readablecode.ThePythoninterpreterautomaticallyenforcescorrectindentation,whereastheJavacompilerdoesnot.WithJava,youneedanadd-onproductsuchastheJalopycodeformattertoprovideautomatedenforcementofindentationstandards.APPENDIX:Aboutstaticvs.dynamictyping,andstrongvs.weaktyping,ofprogramminglanguages.[/b]Thereiswidespreadconfusionordisagreementaboutthemeaningsofthewordsstatic,dynamic,strongandweakwhenusedtodescribethetypesystemsofprogramminglanguages.Whatfollowsisadescriptionoftheway(oratleastoneoftheways)thesetermsaremostcommonlyused.

Inastaticallytypedlanguage,everyvariablenameisboundboth(1)toatype(atcompiletime,bymeansofadatadeclaration)and(2)toanobject.Thebindingtoanobjectisoptional—ifanameisnotboundtoanobject,thenameissaidtobenull.Onceavariablenamehasbeenboundtoatype(thatis,declared)itcanbebound(viaanassignmentstatement)onlytoobjectsofthattype;itcannoteverbeboundtoanobjectofadifferenttype.Anattempttobindthenametoanobjectofthewrongtypewillraiseatypeexception.

Inadynamicallytypedlanguage,everyvariablenameis(unlessitisnull)boundonlytoanobject.Namesareboundtoobjectsatexecutiontimebymeansofassignmentstatements,anditispossibletobindanametoobjectsofdifferenttypesduringtheexecutionoftheprogram.

Hereisanexample.Inastatically-typedlanguage,thefollowingsequenceofstatements(whichbindsanintegerobject,thenastringobject,tothenameemployeeName)isillegal.IfemployeeNamehadbeendeclaredtobeanint,thenthesecondstatementwouldbeillegal;ifithadbeendeclaredtobeaString,thenthefirststatementwouldbeillegal.Butinadynamically-typedlanguagethissequenceofstatementsisperfectlyfine.

employeeName=9

employeeName="SteveFerg"

Pythonisadynamically-typedlanguage.Javaisastatically-typedlanguage.Inaweaklytypedlanguage,variablescanbeimplicitlycoercedtounrelatedtypes,whereasinastronglytypedlanguagetheycannot,andanexplicitconversionisrequired.(NotethatIsaidunrelatedtypes.Mostlanguageswillallowimplicitcoercionsbetweenrelatedtypesa€”forexample,theadditionofanintegerandafloat.ByunrelatedtypesImeanthingslikenumbersandstrings.)Inatypicalweaklytypedlanguage,thenumber9andthestring"9"areinterchangeable,andthefollowingsequenceofstatementsislegal.

a=9

b="9"

c=concatenate(a,b)//produces"99"

d=add(a,b)//produces18

Inastronglytypedlanguage,ontheotherhand,thelasttwostatementswouldraisetypeexceptions.Toavoidtheseexceptions,somekindofexplicittypeconversionwouldbenecessary,likethis.

a=9

b="9"

c=concatenate(str(a),b)

d=add(a,int(b))

BothJavaandPythonarestronglytypedlanguages.ExamplesofweaklytypedlanguagesarePerlandRexx.Athirddistinctionmaybemadebetweenmanifestlytypedlanguagesinwhichvariablenamesmusthaveexplicittypedeclarations,andimplictlytypedlanguagesinwhichthisisnotrequired.Moststaticlanguagesarealsomanifestlytyped(Javacertainlyis),butFrankMitchellnotesthatsomearenot:"HaskellandthedialectsofML,forexample,caninferthetypeofanyvariablebasedontheoperationsperformedonit,withonlyoccasionalhelpfromanexplicittype."////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////JavaPythonUsedtobe"JPython",namerecentlychangedto"jython".AnimplementationofthePythonLanguagethatgeneratesbytecodesfortheJavavirtualmachine.http://www.jython.org/
fromthesite...(somefromanoldersite)Jythonisanimplementationofthehigh-level,dynamic,object-orientedPythonLanguagewrittenin100%PureJava,andseamlesslyintegratedwiththeJavaplatform.ItthusallowsyoutorunPythononanyJavaplatform.Jythonisfreelyavailableforbothcommercialandnon-commercialuseandisdistributedwithsourcecode.JythoniscomplementarytoJavaandisespeciallysuitedforthefollowingtasks:Embeddedscripting-JavaprogrammerscanaddtheJPythonlibrariestotheirsystemtoallowenduserstowritesimpleorcomplicatedscriptsthataddfunctionalitytotheapplication.SinceJPythoniscertified100%PureJava,itcanbeaddedtoanapplicationwithoutfearofcompromisingitsabilitytorunonallJavaplatforms.
Interactiveexperimentation-JythonprovidesaninteractiveinterpreterthatcanbeusedtointeractwithJavapackagesorwithrunningJavaapplications.ThisallowsprogrammerstoexperimentanddebuganyJavasystemusingJython.
Rapidapplicationdevelopment-PythonLanguageprogramsaretypically2-10XshorterthantheequivalentJavaprogram.Thistranslatesdirectlytoincreasedprogrammerproductivity.TheseamlessinteractionbetweenPythonLanguageandJavaallowsdeveloperstofreelymixthetwolanguagesbothduringdevelopmentandinshippingproducts.

Strengths:Abilitytouseascriptinglanguagefromwithinjava.Thisalonemakesitworthwhile!
ExcellentabilitytoinvokeJavaobjectsfromPythoncode.Thismeansthatyouhaveeasyaccesstoallthosejavalibraries.Infact,it'softenEASIERtocalljavaobjectsfromthePythonsidethanfromthejavaside!Theonlytimeitgetsannoyingiswhentherearemultiplemethodswiththesamenamebutmultiplesignatures.
PrettydarneasytoinvokePythonobjectsfromJavacode.Thislessused,butvitallyimportantforcompleteintegration.
Allthe"obvious"conversionsareperformedforyou.Strings,numbers,arrays,andthingslikethataretypicallyconvertedforyouwithlittleeffort.Ajava.lang.StringjustbecomesaPythonstring(andvice-versa)withnoneedto"convert".Withfancierobjectsyou'llneedtomakesomeeffort.
PythoninterpretercaneasilybeembeddedinJava.Theexistanceof"exec"(orit'sequivalent)inPerlLanguage,PythonLanguage,LispLanguage,etcmakesitquiteeasytomakethingsuser-scriptable(atruntime).NowyoucandoitforJavaLanguagetoo,onlytheuserscriptsgetwritteninpython.
Weaknesses:Classloadingisweak.Forexample,ifyouchangeascript,youeitherneedtorunitwithanewclassloaderorrestarttheapplicationthatwillexecthescript.Furthermore,reloadisshallow,soifanyimportedscriptschange,theyalsoneedtoberecompiledandrununderanewclassloader.
JythonprogramsrunmuchmoreslowlythanCPythonones.
JythonisaboutonetenthofaversionorsobehindCPython,plusitdoesn'thaveallthesamelibrariesandfunctionalityasCPython.
Javaarraysareaproblem.UsethejarraymoduleforJavaarraysupport.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

WhatarethecriteriaIshouldconsiderwhendecidingbetweenNumericPython,MatlaborOctave?

Jan24th,200108:25MarcelOliver,LouisLuang

[Note:Thisisacomplicatedquestion.Iamcurrentlytryingmakethisdeterminationformyself,too.ThisiswhatIcameupwithafterabitofsearchingandtrying.Hopefullymoreknowlegeablepeoplewilladdsomemeat.]

MathematicalFeatures:

-CurrentlyMatlabsetsthestandard.OctaveistrailingMatlabbyseveralversions.ThemaingistbehindOctaveistoprovideafreeimplementationofMatlab.

-Numpyhasasetofbasicfeaturesthatcovermostofwhatisrequiredforastandardundergraduatenumericalanalysiscurriculum,(standardnumericallinearalgebra,FFT)butnotmuchmore.Fancystufflikedomaintriangulationsisnotsupportedanddoesnotseemcurrentlyavailable.[Don'tknowOctave'sstatusonthisparticularissue.]

-Therearesomebindingstostandardnumericallibraries,e.g.Multipack[Linkhttp://oliphant.netpedia.netiscurrentlybroken]

GraphicalCapabilities:

-Again,Matlabisstateoftheart.

-AfrequentcriticismaboutOctaveisthatitsgraphicalcapabilitiesaresubstandard,inparticularwithregardstopublicationquality3Dgraphics.[Currentstatus?]

-Therearegraphicaladd-onsfornumpy[Noexperiencewithany.]

InterfacestoExternalCode:

-AllthreearesufficientlyabletointerfacewithexternalCorFortrancode.

ProgrammingLanguage:

-Numpybuildsuponattractivegeneral-purposeobject-orientedprogramminglangage.

-OctaveandMatlabsharemostlythesamespecialpurposelanguage.MaybesecondweakestpointofMatlabafterLicencing.

-SomeclumsynessinNumpywithMatrixmultiplication.Maydisappearatsomepoint,seehttp://python.sourceforge.net/peps/pep-0211.htmlhttp://python.sourceforge.net/peps/pep-0225.html

-ExistingPhythonmodulesshouldmakeiteasytointerfacewithInternetorlow-levelI/Oifsodesired.

Documentation:

-Matlab:Lotsofbooksandinternetresourcesavailable.

-Octave:SomeMathlabinfomaywork,somewhatcompleteusermanual,butsomewhatoutdated.

-Numpy:ManygoodbooksonPythoningeneral,arathershortbutup-to-dateintroductiontoNumpy.

Portability:

-NumpyandOctave;generallygood[Knownproblems?]

-Matlab:AnyplatformsthatMathworksseesfittosupport.Thiscurrentlyexcludesallnon-IntelLinuxports.

Lincense:

-Matlab:proprietary.

-Octave:GPL

-Numpy:PhythonLincense,isconsideredfree.

Conclusion:

IcurrentlyplantogiveNumpyatryasbothateachingplatformandfordoingsmalltoy-caseresearchcodes.Iamnotyetsurehowthiswillworkout,butIdecidedfortheprobablyleast-establishedoptionforthefollowingreasons.

-Afterfallingintotheproprietarytrapwithawell-knowprogramforsymbolicmath,Idonotwanttorepeatthisexperience.

-PythonasalanguageasanaesteticappealthatMatlab/Ocatvesimplydonothave.Further,thelanguageisusefulfarbeyondnumericalmath,whichisabigbonuswhenusingitasateachinglanguage.

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////PyMat-AninterfacebetweenPythonandMATLAB

Introduction

NumPyisasetofnumericalextensionsforPythonthatintroducesamultidimensionalarraytypeandarichsetofmatrixoperationsandmathematicalfunctions.UserswhohaveMATLAB5installed,however,maywishtotakeadvantageofsomeofMATLAB'sadditionalfunctions,includingtheplottinginterface.ThePyMatmoduleactsasaninterfacebetweenNumPyarraysinPythonandaMATLABenginesession,allowingarraystobepassedbackandforthandarbitrarycommandstobeexecutedintheMATLABworkspace.PyMatisusableonbothUNIXandWin32platforms,althoughtherearesomeslightdifferencesbetweenthetwo(mainlyduetoMATLAB'slimitations).YoucandownloadthelatestversionofPyMatfrom:

http://claymore.engineer.gvsu.edu/~steriana/Python

Functions

open([startcmd])

ThisfunctionstartsaMATLABenginesessionandreturnsahandlethatisusedtoidentifythesessiontoallotherPyMatfunctions.Thehandleisofintegertype.OntheWin32platform,theoptionalparameter

startcmd

isalwaysignored.OnUNIXplatforms,itindicatesthemethodofstartingMATLAB.Quotingfromthedocumentationforthe

engOpen

functionfromtheMATLABAPIreferencemanual:OnUNIXsystems,if

startcmd

isNULLortheemptystring,

engOpen

startsMATLABonthecurrenthostusingthecommand

matlab

.If

startcmd

isahost-name,

engOpen

startsMATLABonthedesignatedhostbyembeddingthespecifiedhostnamestringintothelargerstring:

"rshhostname/"/bin/csh-c'setenvDISPLAYhostname:0;matlab'/""

startcmd

isanyotherstring(haswhitespaceinit,ornonalphanumericcharacters),thestringisexecutedliterallytostartMATLAB.OnUNIXsystems,

engOpen

performsthefollowingsteps:1.Createstwopipes.2.ForksanewprocessandsetsupthepipestopassstdinandstdoutfromMATLAB(parent)totwofiledescriptorsintheengineprogram(child).3.ExecutesacommandtorunMATLAB(

rsh

forremoteexecution).UnderWindowsonaPC,

engOpen

opensanActiveXchanneltoMATLAB.ThisstartstheMATLABthatwasregisteredduringinstallation.Ifyoudidnotregisterduringinstallation,onthecommandlineyoucanenterthecommand:

matlab/regserver

close(handle)

ThisfunctionclosestheMATLABsessionrepresentedby

handle

eval(handle,string)

ThisfunctionevaluatesthegivenstringintheMATLABworkspace.Essentially,itisasifyouhadtypedthestringdirectlyinMATLAB'scommandwindow.Notethatthisfunctionalwayssucceedswithoutanyexceptionsunlessthehandleisinvalid,eveniftheevaluationfailedintheMATLABworkspace!.Youareresponsibleforverifyingsuccessfulexecutionofyourcode.

get(handle,name)

ThisfunctionretrievesamatrixfromMATLAB'sworkspaceandreturnsaNumPyarraywiththesameshapeandcontents.The

name

parameterspecifiesthenameofthearrayinMATLAB'sworkspace.Currently,onlyone-dimensionalandtwo-dimensionalfloating-pointarrays(realorcomplex)aresupported.Structures,cellarrays,multi-dimensionalarrays,etc.arenotyetsupported.OnUNIXsystems,thisfunctioncanalsobeusedtoretrievecharacterstrings,inwhichcaseaPythonstringobjectisreturned.ThisfunctionalityisnotsupportedonWin32(duetoMATLABrestrictions).

put(handle,name,data)

ThisfunctionplacesaPythonobjectintoMATLAB'sworkspaceunderthegivenname.The

data

parametercanbeoneofthreethings:ANumPyarray--inthiscase,anarrayofthesameshapeandcontentswillbeplacedintotheMATLABworkspace.TheMATLABarraywillbeindouble-precisionformat(realorcomplex),convertingfromtheNumPyarraytypeasnecessary.Onlyone-dimensionalortwo-dimensionalNumPyarraysaresupported.
APythonlistortuplecontainingnumericvalues.Inthiscase,aNumPyobjectiscreatedfromthelistortuple(asifyouwereusingNumPy's

array()

function)andthatobjectisinstantiatedinMATLAB'sworkspace.
APythonstringobject.Inthiscase,aMATLABcharacterarraywillbeinstantiatedwiththecontentsofthestring.

Limitations

ThefollowinglimitationsapplytothecurrentversionofPyMat:Only1-Dand2-Ddouble-precision(realorcomplex)MATLABarraysaresupported(andsinglecharacterstrings).Matricesofhigherdimension,structurearrays,cellarrays,etc.arenotyetsupported.
TheWin32platformdoesnotsupportretrievingcharacterstringsfromtheMATLABworkspace.

Examples

HereisasimpleexamplethatcomputestheDiscreteCosineTransformofashortNumPyarrayusingMATLAB's

dct

function:

>>>importpymat

>>>fromNumericimport*

>>>x=array([1,2,3,4,5,6])

>>>H=pymat.open()

>>>pymat.put(H,'x',x)

>>>pymat.eval(H,'y=dct(x)')

>>>printpymat.get(H,'y')

[8.57321410e+00-4.16256180e+00-1.55403172e-15-4.08248290e-01-1.88808530e-15-8.00788912e-02]

>>>pymat.close(H)

Installation

Win32
Simplyplacethe

pymat.pyd

filesomewhereonyourPythonsearchpath.AlsoensurethatMATLAB's

BIN

directoryissomewhereonyourDOSpath,orelsethatyouhavecopiedMATLAB's

LIBENG.DLL

and

LIBMX.DLL

filessomewhereonthispath.///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////Alightweightlanguagehasonedatastructureandusesitwell.Perl,TCL-StringPython,Scheme-ListMatlab-MatrixAllofthese(well,Idon'tactuallyknowTCLandPerl)offerotherdatatypes,butifyouusethepredominantdatatypethingsgomuchmoresmoothly.ThekeyisthatwhenthereisoneformofI/O,youcanhooklotsofthingstogethereasily.Aspointedoutattheconference,thistradesshorttermeaseofuseagainstlong-termmaintainability.

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