What Is Computer Science? Molly A. O Neil CS 2308 Spring 2016

Transcription

1 What Is Cmputer Science? Mlly A. O Neil CS 2308 Spring 2016

2 But first: what is CS nt? Cmputer Science!= Prgramming (Really.) What Is CS? 2

3 Still nt cmputer science Sftware develpment & testing Server administratin Infrmatin technlgy (IT) management Building a cmputer hardware Like prgramming, cmputer scientists may d sme r all f these things What Is CS? 3

4 CS & prgramming Cmputer science is n mre abut cmputers than astrnmy is abut telescpes. [Edsger Dijkstra (maybe)] Prgramming is a tl used t d CS Why d we write cde? T autmate the slving f a prblem (r the transfrming f infrmatin frm ne frm t anther) that wuld be difficult r impssible t slve (transfrm) by hand What Is CS? 4

5 Cmputer Science, defined: My definitin: Cmputer Science is the study f cmputatin and its applicatins t prblem-slving Mre frmally: Cmputer science is the systematic study f the feasibility, structure, expressin, and mechanizatin f the algrithms that underlie the the acquisitin, representatin, prcessing, strage, cmmunicatin f, and access t infrmatin. [Wikipedia] What Is CS? 5

6 An algrithm is A prcess r set f rules t be fllwed in calculatins r ther prblem-slving peratins, especially by a cmputer [Oxfrd Dictinaries] A prcedure fr slving a mathematical prblem in a finite number f steps that frequently invlves repetitin f an peratin; bradly: a step-by-step prcedure fr slving a prblem [Merriam-Webster] What Is CS? 6

7 Algrithms & prblem-slving An algrithm is a well-defined sequence f cmputatinal steps t transfrm sme input value (r set f values) int an utput value (r set f values) using finite resurces In rder t autmate the slving f a prblem with a cmputer, we first must: Understand the prblem Develp a step-by-step prcedure by which the prblem can be slved Evaluate whether the prcedure cnsumes a reasnable amunt f resurces What Is CS? 7

8 Cmplexity & sme questins Cmputer Science is als the study f cmplexity Hw can this prblem be slved? Can it be slved at all? (Sme prblems can be prven nn-cmputable; sme slutins have intractable running times) Can yu create an autmatable, step-by-step prcess t slve the prblem? Is this the best slutin? (And what des best even mean?) Is it the fastest slutin? The slutin that requires the least memry? That cnsumes the least pwer r energy? What Is CS? 8

9 Cmplexity & sme questins Cmputer Science is als the study f cmplexity Hw can this prblem be slved? Can it be slved at all? (Sme prblems can be prven nn-cmputable; sme slutins have intractable running times) Can yu create an autmatable, step-by-step prcess t slve the prblem? Is this the best slutin? (And what des best even mean?) Is it the fastest slutin? The slutin that requires the least memry? That cnsumes the least pwer r energy? ß Only this ne is prgramming! What Is CS? 9

10 N algrithms fr M prblems There are usually many algrithms t slve a particular prblem Sme may be gd, sme may be bad (Again, what d these wrds even mean? Sme may be t slw, sme may require string t much state ) Hw t chse the best? Smetimes a single algrithm can be applied t slve multiple prblems What Is CS? 10

11 What this means fr yu in CS1 r 2 Learn the syntax and semantics f C++, but Always start with the prblem-slving! Every assignment is a prblem t slve Start with a whitebard r pencil/paper What are the steps required t slve the prblem? What des yur cde need t d? Eventually: Will yur cde perfrm well enugh? What Is CS? 11

12 A (very brief) early histry 1804: Jseph-Marie Jacquard invents a lm that can weave cmplicated patterns described by hles punched in cards 1837: Charles Babbage describes an Analytical Engine with memry, an arithmetic unit, and ability t interpret a prgramming language with lps and cnditinals. His friend, the mathematician and writer Ada Lvelace, writes a reprt describing his machine and designing the first algrithm intended t be executed n it : Alan Turing cnstructs the first frmal mdel f a cmputer and shws that there are prblems his machine cannt slve (e.g., the halting prblem) What Is CS? 12

13 A (very brief) early histry, part II 1947: The inventin f the transistr 1940s: Military cdebreaking and ballistics calculatins drive the develpment f several cmputatinal machines, including the ENIAC (ne f the first general-purpse cmputers) 1951: Grace Hpper invents the ntin f a cmpiler, allwing the develpment f high-level languages What Is CS? 13

14 What s the cmmn thread between these inventins? The general-purpse cmputer as we knw it hadn t been invented yet What Is CS? 14

15 What s the cmmn thread between these inventins? The general-purpse cmputer as we knw it hadn t been invented yet Yu dn t need a cmputer t d cmputer science! What Is CS? 15

16 CS is a huge field In rugh rder frm theretical t applied Algrithms, Cmputatin, & Cmplexity Thery Fcused n answering fundamental questins abut what prblems are cmputable and what resurces are required t perfrm thse cmputatins Infrmatin & Cding Thery Studies the prperties f systems that cnvert infrmatin frm ne frm t anther and their theretical limits (e.g., data cmpressin, cryptgraphy, errr detectin and crrectin, data transmissin ver a netwrk) Prgramming Languages Cncerned with the design, implementatin, and frmal prperties f languages that allw humans t express algrithmic instructins t cmputers What Is CS? 16

17 CS is a huge field (cntinued) Artificial Intelligence & Machine Learning Devises prcesses by which cmputers can perfrm tasks requiring decisin-making, learning, envirnmental adaptatin, and/r cmmunicatin Databases, Data Mining, & Big Data Studies methds fr string and efficiently searching, retrieving, and discvering patterns in (increasingly vast amunts f) data Cmputer Security & Cryptgraphy Attempts t prtect infrmatin frm unauthrized access r mdificatin while retaining accessibility fr authrized users What Is CS? 17

18 CS is a huge field (cntinued) Cmputatinal Science Cncerned with cnstructing techniques by which cmputers can slve scientific prblems acrss many dmains, ften thrugh cmputer simulatin (e.g., cmputatinal physics, biinfrmatics) Cmputer Graphics & Visualizatin Studies methds fr synthesizing and manipulating visual cntent as well as prcessing and analyzing images t cnvert them t infrmatin (e.g., cmputer visin) Operating Systems & Cmpilers Cncerned with the develpment and structure f prgrams that manage the interactins f a cmputer s hardware and sftware resurces, and with the develpment f prgrams t translate high-level cde int ptimized machine instructins What Is CS? 18

19 CS is a huge field (cntinued) Parallel & Distributed Systems Studies the prperties and design f cmputatinal tasks that can be brken dwn int several independent subtasks, and the design and implementatin f systems capable f executing these sub-tasks cncurrently while allwing inter-prcess cmmunicatin Cmputer Architecture & Cmputer Engineering Fcuses n imprving the design and implementatin f cmputer systems t enable brader classes f prblem t be slved Sftware Engineering Applies rigrus engineering techniques t the design, develpment, testing, and maintenance f large sftware prjects What Is CS? 19

20 CS is a huge field (cntinued) Parallel & Distributed Systems Studies the prperties and design f cmputatinal tasks that can be brken dwn int several independent subtasks, and the design and implementatin f systems capable f executing these sub-tasks cncurrently while allwing inter-prcess cmmunicatin Cmputer Architecture & Cmputer Engineering Fcuses n imprving the design and implementatin f cmputer systems t enable brader classes f prblem t be slved Sftware Engineering this wasn t even clse t an exhaustive list Applies rigrus engineering techniques t the design, develpment, testing, and maintenance f large sftware prjects What Is CS? 20

21 A few cl algrithms ( described much t quickly) What Is CS? 21

22 PageRank [Sergey Brin & Larry Page, 1998] The prblem: Hw t determine the imprtance f webpages s search results can be rdered The key insight: If a lt f ther webpages link t a particular page, that page is likely imprtant The algrithm: Assign each page an initial equal rank, essentially a prbability f a persn wh is clicking n randm links arriving at the page Over many iteratins hi- res.png Each pages transfers a fractin f its rank t all the utbund linked pages Stp iterating when the page ranks (prbabilities) cnverge, i.e. stp changing What Is CS? 22

23 Barnes Hut [Jsh Barnes & Piet Hut, 1986] The prblem: Simulating the interactins f stars in a galaxy requires cmputing the frce applied t every star by every ther star The key insight: Tw stars that are very far frm ne anther dn t exert much frce n ne anther individually, but rather as ne part f a nearby cluster f stars The algrithm: Tree_partitining_f_100_bdies.png Divide the space arund all the stars int a hierarchy f cubic cells, where cells higher up the hierarchy represent grupings f multiple stars r sub-cells Cmpute the center f gravity f each cell When calculating star-pair frce interactins, nly nearby stars need t be treated individually. Stars in distant cells can be treated as the center f gravity f the entire cluster What Is CS? 23

24 Ant Clny Optimizatin [Marc Drig, 1992] The prblem: Find a gd path thrugh a graph (e.g., find the rder in which t visit N cities and return t starting city, traveling the shrtest ttal distance) The key insight: Ants travel randmly lking fr fd. When they find sme, they return t their clny, laying phermne n the rute. If anther ant finds the trail, it is likely t fllw it rather than wandering randmly. Phermne evaprates ver time, s the lnger the trail, the mre phermne will evaprate in the time it takes an ant t mve back and frth. Phermne density will accumulate n shrt paths mre than n lng nes The algrithm: With many cde threads running in parallel, simulate this behavir by having each thread traverse the graph lking fr better rutes Threads increase the weight n graph edges that appear in gd slutins What Is CS? 24

25 Sme recent prblems CS has slved ( Slved? Slved well enugh fr nw?) What Is CS? 25

26 Diagnsing cancer IBM Watsn: supercmputer capable f natural language prcessing, infrmatin retrieval frm TB f data, and machine learning Current prject: Find persnalized treatments fr cancer patients by cmparing treatment and disease histries, symptms, scans, and genetic data with huge quantities f medical literature Watsn can make treatment recmmendatins in minutes based n data analysis that wuld take weeks fr a team f human researchers Success rate f 90% in diagnsing lung cancer, cmpared t 50% fr human dctrs [ What Is CS? 26

27 Image lcatin sleuthing Graphics researchers develped an algrithm that can analyze the distributin f texture, clr, and lines in a pht and identify where the pht was taken (by searching fr phts with a similar appearance in GPS-tagged images n Flickr) Applicatins: Image search Frensics [ [ negie-melln- algrithm-pinpints-pht-image-lcati ns.html] What Is CS? 27

28 Terrrist netwrk mapping Scial Netwrk Analysis (SNA) applies netwrk and graph thery t scial structures, such as friend and cntact netwrks, disease transmissin, etc. Algrithms have been develped t identify ndes with high centrality: ndes cnnected t the mst ther ndes, ndes that are n the mst shrtest paths between ther ndes, critical ndes that bridge therwise uncnnected sub-netwrks, etc. Fr example, if yu can identify central ndes using the cmmunicatin recrds f suspected terrrists, yu may be able t identify the leadership and whm t target t dismantle the netwrk Has been retractively applied t identify the 9/11 hijackers What the NSA is ding with all that cmmunicatins data it cllects? [ What Is CS? 28

29 Acknwledgments Intrductin t CS, CS 5, Harvey Mudd 5_gld_mrn.pptx What is Cmputer Science? A Very Brief Histry f Cmputer Science, Jeffrey Shallit Tp 10 Wicked Cl Algrithms, Michael Cney What Is CS? 29