Presentation on theme: "Half-life of knowledge"— Presentation transcript:
1Half-life of knowledge Hari V SahasrabuddheKanwal Rekhi School of I.T., IITB
2what is half-life?Definition: The time required for the quantity of a chemical, drug or radioisotope to fall to half. For example, if the quantity now is 32, and half-life is 10 days, the quantity will be 16 after 10 days, 8 after 10 more days, etc.
3First used “Half-life of knowledge” Fritz Machlup( )
5Does knowledge decay like that? No, but it may become useless when the situation changes
6A progression of terms Data: factual information, often numeric Information: specific knowledgeKnowledge: familiarity, awareness, understandingWisdom: insight, ability to judgeOur use of “knowledge” is a bit fuzzy – it fits somewhere in this progression.
7What is new in Oracle9i?Oracle Streams (replace Oracle Advance Replication and Standby Databases)Cluster file system for Windows and Linux (raw devices are no longer required)(etc.)
8MySQL: Changes in 5.0.2Warning: Incompatible change! NOT a BETWEEN b AND c is parsed as NOT (a BETWEEN b AND c) rather than as (NOT a) BETWEEN b AND c
10Even mathematics!Is mathematics necessary? Moving Beyond Myths, published by the National Academy of Sciences, says so, but Prof. Dudley of DePauw University does not agree!(See references)
11Halting problem - definition Given a description of an algorithm and its initial input, determine whether the algorithm, when executed on this input, ever halts (completes). The alternative is that it runs forever without halting.
12Halting problem - answer Alan Turing proved in 1936 that a general algorithm to solve the halting problem for all possible inputs cannot exist. We say that the halting problem is undecidable.
13Halting problem – informal proof Let P be a program that reads any program Q and prints 1 if Q halts, 0 if not.Define P’:read program Qsimulate P on input Qif output of step 2 is = 1, go to step 2HaltWhat happens when P’ is fed to P’?
14Halting problem – formal proof Turing’s formal proof is based on Turing Machine, a model of computation with a finite controller coupled to a unbounded memory
15Another model of computation -calculusAllows us to define a recursive functionFoundation for LISP class of programming languages
16Decidable but hard problems Hamiltonian circuit: a circuit that visits all vertices of a given graphWe don’t know how to find one in any arbitrary graph in time limited by a polynomial, any polynomial, of the number of vertices.If you can solve that one, a number of other problems are solved!
17Hard - example Remember Cramer’s rule? n*n determinant => n (n-1)*(n-1) determinantsTime for n*n determinant equals roughly n*time for an (n-1)*(n-1) determinantA PC which can calculate a 2*2 determinant in 0.5*10-9 seconds needs almost 1 year to calculate a 19*19 determinant by Cramer’s rule, and 19 years for a 20*20 determinant!
18Hard example contd.We could use a supercomputer. A 60 teraflop supercomputer can calculate a 19*19 determinant in less than 17 hours (but even it will need about 18 years for a 22*22 determinant)So, faster computers do not compensate for algorithmic complexity
19First programmerCharles Babbage described his analytical engine in 1834, and in Lady Lovelace either created or corrected a program for it to compute Bernoulli numbers (first defined in print in 1713)(The analytical engine could never actually be built.)
20How many programming languages are there? Thousands of them!Main typesImperative (c, c++, java, …)Functional (LISP, SCHEME) and applicative (APL)Declarative (PROLOG)
21BCS: Future challenges Conference: Brit. Comp. Soc., March 2004Two separate reports, on “Grand Challenges” in education and researchEither report identifies seven challengesMost challenges arise from spread of computing to new areas, e.g. embedded systems, memories for life
22Identifying lasting knowledge Abstract rather than concreteTechnology-independent areas, e.g. maths, theoretical CS, architecture, …Older, still useful knowledge(if it survived n years it might survive n more years)
23What after you graduate? Self-study and reference skillslibrary, bookstores, search engines, …List of references is availableThese were gathered using web search