Applied Mathematical Sciences Volume 127 Editors S.S.Antman J.E.Marsden L.Sirovich Advisors J.K.Hale P.Holmes J.Keener J.Keller B.J.Matkowsky A.Mielke C.S.Peskin K.R.Sreenivasan Applied Mathematical Sciences 1. John:PartialDifferentialEquations,4thed. 33. Grenander:RegularStructures:LecturesinPattern 2. Sirovich:TechniquesofAsymptoticAnalysis. Theory,Vol.III. 3. Hale:TheoryofFunctionalDifferentialEquations, 34. Kevorkian/Cole:PerturbationMethodsinApplied 2nded. Mathematics. 4. Percus:CombinatorialMethods. 35. Carr:ApplicationsofCentreManifoldTheory. 5. vonMises/Friedrichs:FluidDynamics. 36. Bengtsson/Ghil/Ka¨lle´n:DynamicMeteorology: 6. Freiberger/Grenander:AShortCoursein DataAssimilationMethods. ComputationalProbabilityandStatistics. 37. Saperstone:SemidynamicalSystemsinInfinite 7. Pipkin:LecturesonViscoelasticityTheory. DimensionalSpaces. 8. Giacaglia:PerturbationMethodsinNon-linear 38. Lichtenberg/Lieberman:RegularandChaotic Systems. Dynamics,2nded. 9. Friedrichs:SpectralTheoryofOperatorsinHilbert 39. Piccini/Stampacchia/Vidossich:Ordinary Space. DifferentialEquationsinRn. 10. Stroud:NumericalQuadratureandSolutionof 40. Naylor/Sell:LinearOperatorTheoryin OrdinaryDifferentialEquations. EngineeringandScience. 11. Wolovich:LinearMultivariableSystems. 41. Sparrow:TheLorenzEquations:Bifurcations, 12. Berkovitz:OptimalControlTheory. Chaos,andStrangeAttractors. 13. Bluman/Cole:SimilarityMethodsforDifferential 42. Guckenheimer/Holmes:NonlinearOscillations, Equations. DynamicalSystems,andBifurcationsofVector 14. Yoshizawa:StabilityTheoryandtheExistenceof Fields. PeriodicSolutionandAlmostPeriodicSolutions. 43. Ockendon/Taylor:InviscidFluidFlows. 15. Braun:DifferentialEquationsandTheir 44. Pazy:SemigroupsofLinearOperatorsand Applications,3rded. ApplicationstoPartialDifferentialEquations. 16. Lefschetz:ApplicationsofAlgebraicTopology. 45. Glashoff/Gustafson:LinearOperationsand 17. Collatz/Wetterling:OptimizationProblems. Approximation:AnIntroductiontotheTheoretical 18. Grenander:PatternSynthesis:LecturesinPattern AnalysisandNumericalTreatmentofSemi-Infinite Theory,Vol.I. Programs. 19. Marsden/McCracken:HopfBifurcationandIts 46. Wilcox:ScatteringTheoryforDiffractionGratings. Applications. 47. Hale/Magalha˜es/Oliva:DynamicsinInfinite 20. Driver:OrdinaryandDelayDifferentialEquations. Dimensions,2nded. 21. Courant/Friedrichs:SupersonicFlowandShock 48. Murray:AsymptoticAnalysis. Waves. 49. Ladyzhenskaya:TheBoundary-ValueProblemsof 22. Rouche/Habets/Laloy:StabilityTheoryby MathematicalPhysics. Liapunov’sDirectMethod. 50. Wilcox:SoundPropagationinStratifiedFluids. 23. Lamperti:StochasticProcesses:ASurveyofthe 51. Golubitsky/Schaeffer:BifurcationandGroupsin MathematicalTheory. BifurcationTheory,Vol.I. 24. Grenander:PatternAnalysis:LecturesinPattern 52. Chipot:VariationalInequalitiesandFlowinPorous Theory,Vol.II. Media. 25. Davies:IntegralTransformsandTheir 53. Majda:CompressibleFluidFlowandSystemsof Applications,2nded. ConservationLawsinSeveralSpaceVariables. 26. Kushner/Clark:StochasticApproximationMethods 54. Wasow:LinearTurningPointTheory. forConstrainedandUnconstrainedSystems. 55. Yosida:OperationalCalculus:ATheoryof 27. deBoor:APracticalGuidetoSplines:Revised Hyperfunctions. Edition. 56. Chang/Howes:NonlinearSingularPerturbation 28. Keilson:MarkovChainModels—Rarityand Phenomena:TheoryandApplications. Exponentiality. 57. Reinhardt:AnalysisofApproximationMethodsfor 29. deVeubeke:ACourseinElasticity. DifferentialandIntegralEquations. 30. Sniatycki:GeometricQuantizationandQuantum 58. Dwoyer/Hussaini/Voigt(eds):Theoretical Mechanics. ApproachestoTurbulence. 31. Reid:SturmianTheoryforOrdinaryDifferential 59. Sanders/Verhulst:AveragingMethodsinNonlinear Equations. DynamicalSystems. 32. Meis/Markowitz:NumericalSolutionofPartial DifferentialEquations. (continuedfollowingindex) Victor Isakov Inverse Problems for Partial Differential Equations Second Edition VictorIsakov DepartmentofMathematicsandStatistics TheWichitaStateUniversity Wichita,KS67260-0033 USA [email protected] SeriesEditors: S.S.Antman J.E.Marsden L.Sirovich DepartmentofMathematics ControlandDynamical LaboratoryofApplied and Systems,107-81 Mathematics InstituteforPhysicalScience CaliforniaInstituteof Departmentof andTechnology Technology BiomathematicalSciences UniversityofMaryland Pasadena,CA91125 MountSinaiSchool CollegePark,MD20742–4015 USA ofMedicine USA [email protected] NewYork,NY10029-6574 [email protected] USA [email protected] MathematicsSubjectClassification(2000):35R30,86A22,80A23,78A46,65M32,31B20, 35B60,91B26 LibraryofCongressControlNumber:2005924713 ISBN-10:0-387-25364-5 ISBN-13:978-0387-25364-0 Printedonacid-freepaper. (cid:1)C 2006SpringerScience+BusinessMedia,Inc. Allrightsreserved.Thisworkmaynotbetranslatedorcopiedinwholeorinpartwithoutthewritten permissionofthepublisher(SpringerScience+BusinessMedia,Inc.,233SpringStreet,NewYork, NY10013,USA),exceptforbriefexcerptsinconnectionwithreviewsorscholarlyanalysis.Use in connection with any form of information storage and retrieval, electronic adaptation, computer software,orbysimilarordissimilarmethodologynowknownorhereafterdevelopedisforbidden. Theuseinthispublicationoftradenames,trademarks,servicemarks,andsimliarterms,evenifthey arenotidentifiedassuch,isnottobetakenasanexpressionofopinionastowhetherornottheyare subjecttoproprietaryrights. PrintedintheUnitedStatesofAmerica. (SBA) 9 8 7 6 5 4 3 2 1 springeronline.com To my wife Julie Mostpeople,ifyoudescribeatrainofeventstothem,willtellyouwhattheresult wouldbe.Theycanputthoseeventstogetherintheirminds,andarguefromthem thatsomethingwillcometopass.Therearefewpeople,however,who,ifyoutold themaresult,wouldbeabletoevolvefromtheirowninnerconsciousnesswhat thestepswerewhichleduptothatresult.ThispoweriswhatImeanwhenItalk ofreasoningbackward,oranalytically. —ArthurConanDoyle,AStudyinScarlet Preface to the Second Edition In8yearsafterpublicationofthefirstversionofthisbook,therapidlyprogress- ingfieldofinverseproblemswitnessedchangesandnewdevelopments.Partsof the book were used at several universities, and many colleagues and students as wellasmyselfobservedseveralmisprintsandimprecisions.Someoftheresearch problemsfromthefirsteditionhavebeensolved.Thiseditionservesthepurposes of reflecting these changes and making appropiate corrections. I hope that these additionsandcorrectionsresultedinnottoomanynewerrorsandmisprints. Chapters1and2containonly2–3pagesofnewmateriallikeinsections1.5, 2.5. Chapter 3 is considerably expanded. In particular we give more convenient definition of pseudo-convexity for second order equations and included bound- arytermsinCarlemanestimates(Theorem3.2.1(cid:2))andCounterexample3.2.6.We giveanew,shorterproofofTheorem3.3.1andnewTheorems3.3.7,3.3.12,and Counterexample3.3.9.Werevisedsection3.4,whereanewshortproofofexact observability inequality in given: proof of Theorem 3.4.1 and Theorems 3.4.3, 3.4.4, 3.4.8, 3.4.9 are new. Section 3.5 is new and it exposes recent progress on Carlemanestimates,uniquenessandstabilityofthecontinuationforsystems.In Chapter4weaddedtosections4.5,4.6somenewmaterialonsizeevaluationof inclusionsandonsmallinclusions.Chapter5containsnewresultsonidentification ofanellipticequationfrommanylocalboundarymeasurements(Theorem5.2.2(cid:2), Lemma 5.3.8), a counterexample to stability, a brief description of recent com- pleteresultsonuniquenessofconductivityintheplanecase,somenewresultson identificationofmanycoefficientsandofquasilinearequationsinsectiosn5.5,5.6, andchangesandmostrecentresultsonuniquenessforsomeimportantsystems, likeisotropicelasticitysystems.InChapter7weinformaboutnewdevelopments inboundaryrigidityproblem.Section7.4nowexposesacompletesolutionofthe uniquenessproblemintheattenuatedplanetomographyoverstraightlines(The- orem7.4.1)andanoutlineofrelevantnewmethodsandideas.Insection8.2we giveanewgeneralschemeofobtaininguniquenessresultsbasedonCarlemanes- timatesandapplicabletoawideclassofpartialdifferentialequationsandsystems (Theorem 8.2.2) and describe recent progress on uniqueness problem for linear isotropicelasticitysystem.InChapter9weexpandedtheexpositioninsection9.1 vii viii PrefacetotheSecondEdition to reflect increasing importance of the final overdetermination (Theorems 9.1.1, 9.1.2).Insection9.2weexposenewstabilityestimatefortheheatequationtrans- form (Theorem 9.2.1’ Lemma 9.2.2). New section 9.3 is dedicated to emerging financialapplications:theinverseoptionpricingproblem.Wegivemoredetailed proofsinsection9.5(Lemma9.5.5andproofofTheorem9.5.2).InChapter10we addedabriefdescriptionofanewefficientsinglelayeralgorithmforanimporatnt inverseprobleminacousticsinsection10.2andanewsection10.5onso-called rangetestsfornumericalsolutionsofoverderminedinverseproblems. Manyexerciseshavebeensolvedbystudents,whilemostoftheresearchprob- lemsawaitsolutions.Chapter7ofthefinalversionofthemanuscripthavebeen readbyAlexanderBukhgeim,whofoundseveralmisprintsandsuggestedmany corrections. The author is grateful to him for attention and help. He also thanks the National Science Foundation for long-term support of his research, which stimulatedhisresearchandthewritingofthisrevision. Wichita,Kansas VictorIsakov Preface to the First Edition This book describes the contemporary state of the theory and some numerical aspectsofinverseproblemsinpartialdifferentialequations.Thetopicisofsub- stantialandgrowinginterestformanyscientistsandengineers,andaccordinglyto graduatestudentsintheseareas.Mathematically,theseproblemsarerelativelynew andquitechallengingduetothelackofconventionalstabilityandtononlinearity andnonconvexity.Applicationsincluderecoveryofinclusionsfromanomaliesof their gravitational fields; reconstruction of the interior of the human body from exterior electrical, ultrasonic, and magnetic measurements, recovery of interior structuralparametersofdetailofmachinesandoftheundergroundfromsimilar data (non-destructive evaluation); and locating flying or navigated objects from theiracousticorelectromagneticfields.Currently,therearehundredsofpublica- tions containing new and interesting results. A purpose of the book is to collect and present many of them in a readable and informative form. Rigorous proofs arepresentedwhenevertheyarerelativelyshortandcanbedemonstratedbyquite generalmathematicaltechniques.Also,weprefertopresentresultsthatfromour pointofviewcontainfreshandpromisingideas.Insomecasesthereisnocom- plete mathematical theory, so we give only available results. We do not assume thatareaderpossessesanenormousmathematicaltechnique.Infact,amoderate knowledgeofpartialdifferentialequations,oftheFouriertransform,andofbasic functionalanalysiswillsuffice.However,somedetailsofproofsneedquitespecial andsophisticatedmethods,butwehopethatevenwithoutcompletelyunderstand- ing these details a reader will find considerable useful and stimulating material. Moreover,westartmanychapterswithgeneralinformationaboutthedirectprob- lem, where we collect, in the form of theorems, known (but not simple and not alwayseasytofind)resultsthatareneededinthetreatmentofinverseproblems. Wehopethatthisbook(oratleastmostofit)canbeusedasagraduatetext.Not onlydowepresentrecentachievements,butweformulatebasicinverseproblems, discussregularization,giveashortreviewofuniquenessintheCauchyproblem, andincludeseveralexercisesthatsometimessubstantiallycomplementthebook. Allofthemcanbesolvedbyusingsomemodificationofthepresentedmethods. ix x PrefacetotheFirstEdition Partsofthebookinapreliminaryformhavebeenpresentedasgraduatecoursesat theJohannes-KeplerUniversityofLinz,attheUniversityofKyoto,andatWichita StateUniversity.Manyexerciseshavebeensolvedbystudents,whilemostofthe researchproblemsawaitsolutions.Partsofthefinalversionofthemanuscripthave beenreadbyIlyaBushuyev,AlanElcrat,MatthiasEller,andPeterKuchment,who foundseveralmisprintsandsuggestedmanycorrections.Theauthorisgratefulto thesecolleaguesfortheirattentionandhelp.HealsothankstheNationalScience Foundationforlong-termsupportofhisresearch,whichstimulatedthewritingof thisbook. Wichita,Kansas VictorIsakov