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HD15b.number-theoretic-algorithms

Course: CS 511, Fall 2009
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NumberSystems NumberTheoryAlgorithms ZephGrunschlag CopyrightZephGrunschlag,20012002. Agenda EuclideanAlgorithmforGCD Decimalnumbers(base10) Binarynumbers(base2) Onescomplement Twoscomplement Generalbasebnumbersystems Addition Multiplication Subtraction1sand2scomplement 2 ArithmeticAlgorithms L11 EuclideanAlgorithm m,n Euclidean Algorithm gcd(m,n) integereuclid(pos.integerm,pos.integern) x=m,y=n...

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NumberSystems NumberTheoryAlgorithms ZephGrunschlag CopyrightZephGrunschlag,20012002. Agenda EuclideanAlgorithmforGCD Decimalnumbers(base10) Binarynumbers(base2) Onescomplement Twoscomplement Generalbasebnumbersystems Addition Multiplication Subtraction1sand2scomplement 2 ArithmeticAlgorithms L11 EuclideanAlgorithm m,n Euclidean Algorithm gcd(m,n) integereuclid(pos.integerm,pos.integern) x=m,y=n while(y>0) r=xmody x=y y=r returnx L11 3 gcd(33,77): EuclideanAlgorithm. Example r=xmody x 33 y 77 Step 0 L11 4 gcd(33,77): EuclideanAlgorithm. Example r=xmody 33mod77 =33 x 33 77 y 77 33 Step 0 1 L11 5 gcd(33,77): EuclideanAlgorithm. Example r=xmody 33mod77 =33 77mod33 =11 x 33 77 33 y 77 33 11 Step 0 1 2 L11 6 gcd(33,77): EuclideanAlgorithm. Example r=xmody 33mod77 =33 77mod33 =11 33mod11 =0 x 33 77 33 11 y 77 33 11 0 7 Step 0 1 2 3 L11 gcd(244,117): Step 0 EuclideanAlgorithm. Example r=xmody x 244 y 117 L11 8 gcd(244,117): Step 0 1 EuclideanAlgorithm. Example r=xmody 244mod117=10 x 244 117 y 117 10 L11 9 gcd(244,117): Step 0 1 2 EuclideanAlgorithm. Example r=xmody 244mod117=10 117mod10=7 x 244 117 10 y 117 10 7 L11 10 gcd(244,117): Step 0 1 2 3 EuclideanAlgorithm. Example r=xmody 244mod117=10 117mod10=7 10mod7=3 x 244 117 10 7 y 117 10 7 3 L11 11 gcd(244,117): Step 0 1 2 3 4 EuclideanAlgorithm. Example r=xmody 244mod117=10 117mod10=7 10mod7=3 7mod3=1 x 244 117 10 7 3 y 117 10 7 3 1 L11 12 gcd(244,117): Step 0 1 2 3 4 5 L11 EuclideanAlgorithm. Example r=xmody 244mod117=10 117mod10=7 10mod7=3 7mod3=1 3mod1=0 x 244 117 10 7 3 1 y 117 10 7 3 1 0 13 Bydefinition244and117arerel.prime. EuclideanAlgorithmCorrectness ThereasonthatEuclideanalgorithmworksis gcd(x,y)isnotchangedfromlinetoline.Ifx,y denotethenextvaluesofx,ythen: gcd(x,y)=gcd(y,xmody) =gcd(y,xqy) (theusefulfact) =gcd(y,x)(subtractymultiple) =gcd(x,y) L11 14 EuclideanAlgorithm RunningTime EX:Computetheasymptoticrunningtimeofthe Euclideanalgorithmintermsofthenumberof modoperations: L11 15 EuclideanAlgorithm RunningTime AssumingmodoperationisO(1): integereuclid(m,n) x=m,y=n while(y>0) r=xmody x=y y=r returnx L11 O(1)+ ?(O(1)+ O(1) +O(1) (1)) +O(1) =?O(1) +O Where?isthenumberofwhileloopiterations. 16 EuclideanAlgorithm RunningTime Facts:(x=nextvalueofx,etc.) 2. xcanonlybelessthanyatverybeginningof algorithm oncex>y,x=y>y=xmody 4. Whenx>y,twoiterationsofwhileloopguarantee thatnewxis<originalx becausex=y=xmody.Twocases: I. II. y>xxmody=xy<x yxxmody<yx 17 L11 EuclideanAlgorithm RunningTime (1&2)Afterfirstiteration,sizeofxdecreasesby factor>2everytwoiterations. I.e.after2m+1iterations, x<original_x/2m Q:Whenintermsofmdoesthisprocess terminate? L11 18 EuclideanAlgorithm RunningTime After2m+1steps,x<original_x/2m A:Whileloopexitswhenyis0,whichisright beforewouldhavegottenx=0.Exiting whileloophappenswhen2m>original_x,so definitelyby: m=log2(original_x) Thereforerunningtimeofalgorithmis: O(2m+1)=O(m)=O(log2(max(a,b))) L11 19 EuclideanAlgorithm RunningTime Measuringinputsizeintermsofn=numberofdigitsof max(a,b): n=(log10(max(a,b)))=(log2(max(a,b))) Thereforerunningtimeofalgorithmis: O(log2(max(a,b)))=O(n) (assumednaivelythatmodisanO(1)operation,so estimateonlyholdsforfixedsizeintegerssuchas intsandlongs) L11 20 NumberSystems Q:Whatdoesthestringofsymbols 2134 reallymeanasanumberandwhy? L11 21 NumberSystems A:2thousands1hundreds3tensand4 =2103+1102+3101+4100 ButontheplanetOgg,theintelligentlifeforms haveonlyonearmwith5fingers. L11 22 NumberSystems SoonOgg,numbersarecountedbase5.I.e.on Ogg2134means: 253+152+351+450 Todistinguishbetweenthesesystems,subscripts areused: (2134)10forEarth (2134)5forOgg L11 23 NumberSystems DEF:Abasebnumberisastringofsymbols u=akak1ak2a2a1a0 Withtheaiin{0,1,2,3,,b2,b1}. Thestringurepresentsthenumber (u)b=akbk+ak1bk1+...+a1b+a0 NOTE:Whenb>10,runoutofdecimalnumber symbolssoafter7,8,9usecapitalletters, startingfromA,B,C, L11 24 NumberSystems EG:base2(binary)101,00010 base8(octal)74,0472 base16(hexadecimal)12F,ABCD Q:Computethebase10versionofthese. L11 25 NumberSystems A:base2(binary)101,00010 (101)2=122+021+120=5 (00010)2=0(24+23+22+20)+121=2 base8(octal)74,0472 (74)8=781+480=60 (0472)8=482+781+280=314 base16(hexadecimal)12F,ABCD (12F)16=1162+2161+15160=303 (ABCD)16=10163+11162+12161+13160 L11 26 NumberSystems Binarymostnaturalsystemforbitstringsand hexadecimalcompactifiesbytestrings(1byte=2 hexadecimals) EGinHTML: <fontcolor="ff00ff">NiceColor</font> Q:Whatcolorwillthisbecome? L11 27 NumberSystems A:"ff00ff"representsthergbvalue: Thefirstbyteisforredness,thesecondbyteisfor greenness,andthelastforblueness.TheHTML abovespecifiesthat1516+15=255rednessand bluenessvalues,but016+0=0greenness.Red andbluegivepurple,and255isthetopbrightness sothisisbrightpurple. L11 28 NumberSystems ReverseConversion Convertarbitrarydecimalnumbersintovariousbases, (calculatorfunctionstypicallylimitedtobase2,8, 16and10). EG:BackatOgg.Convert646tobase5.Trytodo alloperationsbase5. L11 29 NumberSystems ReverseConversion BackatOgg.Convert646tobase5.Trytodoall operationsasanOggian(base5): (646)10=(6)10(10)102+(4)10(10)10+(6)10 Eachquantityeasytoconvertintobase5: (6)10=(11)5since6=5+1 (4)10=(4)5 since4<5 (10)10=(20)5 since10=25+0 SoconvertwholeexpressionanddoOggian arithmetic: L11 30 NumberSystems ReverseConversion BackatOgg.Convert646tobase5.Trytodoall operationsasanOggian(base5): (646)10=(11)5(20)52+(4)5(20)5+(11)5 = L11 31 NumberSystems ReverseConversion BackatOgg.Convert646tobase5.Trytodoall operationsasanOggian(base5): (646)10=(11)5(20)52+(4)5(20)5+(11)5 =(11)5(400)5+(130)5+(11)5 = L11 32 NumberSystems ReverseConversion BackatOgg.Convert646tobase5.Trytodoall operationsasanOggian(base5): (646)10=(11)5(20)52+(4)5(20)5+(11)5 =(11)5(400)5+(130)5+(11)5 =(4400)5+(141)5 = L11 33 NumberSystems ReverseConversion BackatOgg.Convert646tobase5.Trytodoall operationsasanOggian(base5): (646)10=(11)5(20)52+(4)5(20)5+(11)5 =(11)5(400)5+(130)5+(11)5 =(4400)5+(141)5 =(10041)5 ThinkinglikeanOggianhurtsbraintoomuch L11 34 NumberSystems ReverseConversion Givenanintegernandabasebfindthestringusuchthat(u) b=n. Pseudocode: stringrepresent(pos.integern,pos.integerb) q=n,i=0 while(q>0) ui=qmodb q=q/b i=i+1 returnuiui1ui2u2u1u0 L11 35 NumberSystems ReverseConversion EG:Convert646toOggian(base5): i ui=qmodb q=q/b 646 L11 36 NumberSystems ReverseConversion EG:Convert646toOggian(base5): i 0 ui=qmodb 646mod5=1 q=q/b 646 646/5=129 L11 37 NumberSystems ReverseConversion EG:Convert646toOggian(base5): i 0 1 ui=qmodb 646mod5=1 129mod5=4 q=q/b 646 646/5=129 129/5=25 L11 38 NumberSystems ReverseConversion EG:Convert646toOggian(base5): i 0 1 2 ui=qmodb 646mod5=1 129mod5=4 25mod5=0 q=q/b 646 646/5=129 129/5=25 25/5=5 L11 39 NumberSystems ReverseConversion EG:Convert646toOggian(base5): i 0 1 2 3 ui=qmodb 646mod5=1 129mod5=4 25mod5=0 5mod5=0 q=q/b 646 646/5=129 129/5=25 25/5=5 5/5=1 L11 40 NumberSystems ReverseConversion EG:Convert646toOggian(base5): i 0 1 2 3 4 L11 ui=qmodb 646mod5=1 129mod5=4 25mod5=0 5mod5=0 1mod5=1 q=q/b 646 646/5=129 129/5=25 25/5=5 5/5=1 1/5=0 41 Readinglastcolumninreverse:10041 NumberSystems InClassExercise Somenumbertheoryfactsarebasedependent.Forexample FirstGradeTeachersRule: Abase10numberisdivisibleby3iffthesumofitsdigitsare. Formally,let n=(ukuk1uk2u2u1u0)10.Then: n mod 3= EG:3|12135because3|(1+2+1+3+5=12) ui i=0 k mod 3 L11 42 ArithmeticalAlgorithms Letswritedownsomefamiliararithmetical algorithms.Conveniently,theyrunthesamein anynumberbase.Insomecases,suchas addition,thereareasymptoticallyfaster approaches,butthesearethesimplest proceduresandtendtobefastestforrelatively small(e.g.<1000bits)numbersizes. L11 43 ArithmeticalAlgorithms Addition Numbersareaddedfromleastsignificantdigitto most,whilecarryinganyoverflowresultingfrom addingacolumn: base10 Carry: x +y L11 base16 7 + 2 4 9 6 0 3 9 + A C 4 B F 0 0 9 44 ArithmeticalAlgorithms Addition Numbersareaddedfromleastsignificantdigitto most,whilecarryinganyoverflowresultingfrom addingacolumn: base10 Carry: x +y L11 base16 1 7 + 2 4 9 6 0 3 9 2 + A C 4 B F 0 0 9 9 45 ArithmeticalAlgorithms Addition Numbersareaddedfromleastsignificantdigitto most,whilecarryinganyoverflowresultingfrom addingacolumn: base10 Carry: x +y L11 base16 1 7 + 2 4 9 6 0 7 3 9 2 + A C 4 B F 0 F 0 9 9 46 ArithmeticalAlgorithms Addition Numbersareaddedfromleastsignificantdigitto most,whilecarryinganyoverflowresultingfrom addingacolumn: base10 Carry: x +y L11 base16 1 1 7 + 2 4 9 3 6 0 7 3 9 2 + A C 4 B F F 0 F 0 9 9 47 ArithmeticalAlgorithms Addition Numbersareaddedfromleastsignificantdigitto most,whilecarryinganyoverflowresultingfrom addingacolumn: base10 Carry: x +y L11 base16 1 1 1 1 7 + 2 0 4 9 3 6 0 7 3 9 2 + A C 6 4 B F F 0 F 0 9 9 48 ArithmeticalAlgorithms Addition Numbersareaddedfromleastsignificantdigitto most,whilecarryinganyoverflowresultingfrom addingacolumn: base10 Carry: x +y L11 base16 1 1 1 1 7 + 1 2 0 4 9 3 6 0 7 3 9 2 + 1 A C 6 4 B F F 0 F 0 9 9 49 ArithmeticalAlgorithms AdditionofPositiveNumbers stringadd(stringsxkxk1x1x0,ykyk1y1y0,intbase) carry=0,xk+1=yk+1=0 for(i=0tok+1) digitSum=carry+xi+yi zi=digitSummodbase carry=digitSum/base returnzk+1zkzk1z1z0 L11 50 1sComplement 2sComplement Thebinarynumbersystemmakessomeoperations especiallysimpleandefficientundercertain representations. Twosuchrepresentationsare 1scomplement 2scomplement Eachmakessubtractionmuchsimpler. Eachhasdisadvantagethatnumberlengthispre determined. L11 51 1sComplement Fixkbits.(EG,k=8forbytes) Representnumberswith|x|<2k1 Leftmostbittellsthesign 1negative(butotherbitschangetoo!) Positivenumbersthesameasstandardbinary 0positive(sopositiveno.sasusual) expansion Negativenumbersgottenbytakingtheboolean complement,hencenomenclature L11 52 1sComplement Examples k=8: 00010010represents18 11101101represents18 Notice:whenaddtheserepresentationsasusualget 11111111,i.e.negative00000000or0=0. Guess:addingnumberswithmixedsignworksthe sameasaddingpositivenumbers Tradeoff:0notunique L11 53 1sComplement Addition Additionisthesameasusualbinaryadditionexcept: ifthefinalcarryis1,cyclethecarrytotheleastsignificantdigit: 00010010represents18,11110011represents12 Sum00000110represents6: Carry: x +y presum overflow answer L11 0 1 0 1 0 1 1 1 0 0 0 0 1 1 0 1 54 1sComplement Addition Additionisthesameasusualbinaryadditionexcept: ifthefinalcarryis1,cyclethecarrytotheleastsignificantdigit: 00010010represents18,11110011represents12 Sum00000110represents6: Carry: x +y presum overflow answer L11 0 1 0 1 0 1 1 1 0 0 0 0 1 1 0 1 1 55 1sComplement Addition Additionisthesameasusualbinaryadditionexcept: ifthefinalcarryis1,cyclethecarrytotheleastsignificantdigit: 00010010represents18,11110011represents12 Sum00000110represents6: Carry: x +y presum overflow answer L11 1 0 1 0 1 0 1 1 1 0 0 0 0 1 1 0 0 1 1 56 1sComplement Addition Additionisthesameasusualbinaryadditionexcept: ifthefinalcarryis1,cyclethecarrytotheleastsignificantdigit: 00010010represents18,11110011represents12 Sum00000110represents6: Carry: x +y presum overflow answer L11 1 0 1 0 1 0 1 1 1 0 0 0 0 1 1 1 0 0 1 1 57 1sComplement Addition Additionisthesameasusualbinaryadditionexcept: ifthefinalcarryis1,cyclethecarrytotheleastsignificantdigit: 00010010represents18,11110011represents12 Sum00000110represents6: Carry: x +y presum overflow answer L11 1 0 1 0 1 0 1 1 1 0 0 0 0 0 1 1 1 0 0 1 1 58 1sComplement Addition Additionisthesameasusualbinaryadditionexcept: ifthefinalcarryis1,cyclethecarrytotheleastsignificantdigit: 00010010represents18,11110011represents12 Sum00000110represents6: Carry: x +y presum overflow answer L11 1 1 0 1 0 1 0 1 1 1 0 0 0 0 0 0 1 1 1 0 0 1 1 59 1sComplement Addition Additionisthesameasusualbinaryadditionexcept: ifthefinalcarryis1,cyclethecarrytotheleastsignificantdigit: 00010010represents18,11110011represents12 Sum00000110represents6: Carry: x +y presum overflow answer L11 1 1 1 0 1 0 1 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 0 1 1 60 1sComplement Addition Additionisthesameasusualbinaryadditionexcept: ifthefinalcarryis1,cyclethecarrytotheleastsignificantdigit: 00010010represents18,11110011represents12 Sum00000110represents6: Carry: x +y presum overflow answer L11 1 1 1 1 0 1 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 0 1 1 61 1sComplement Addition Additionisthesameasusualbinaryadditionexcept: ifthefinalcarryis1,cyclethecarrytotheleastsignificantdigit: 00010010represents18,11110011represents12 Sum00000110represents6: Carry: x +y presum overflow answer L11 1 1 1 1 0 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 0 1 1 62 1sComplement Addition Additionisthesameasusualbinaryadditionexcept: ifthefinalcarryis1,cyclethecarrytotheleastsignificantdigit: 00010010represents18,11110011represents12 Sum00000110represents6: Carry: x +y presum overflow answer L11 1 1 1 1 0 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 0 1 1 1 63 1sComplement Addition Additionisthesameasusualbinaryadditionexcept: ifthefinalcarryis1,cyclethecarrytotheleastsignificantdigit: 00010010represents18,11110011represents12 Sum00000110represents6: Carry: x +y presum overflow answer L11 1 1 1 1 0 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 1 0 1 1 1 0 64 1sComplement Addition Additionisthesameasusualbinaryadditionexcept: ifthefinalcarryis1,cyclethecarrytotheleastsignificantdigit: 00010010represents18,11110011represents12 Sum00000110represents6: Carry: x +y presum overflow answer L11 1 1 1 1 0 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 1 0 1 1 1 1 0 65 1sComplement Addition Additionisthesameasusualbinaryadditionexcept: ifthefinalcarryis1,cyclethecarrytotheleastsignificantdigit: 00010010represents18,11110011represents12 Sum00000110represents6: Carry: x +y presum overflow answer L11 1 1 1 1 0 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 1 0 1 0 1 1 1 1 0 66 1sComplement Addition Additionisthesameasusualbinaryadditionexcept: ifthefinalcarryis1,cyclethecarrytotheleastsignificantdigit: 00010010represents18,11110011represents12 Sum00000110represents6: Carry: x +y presum overflow answer L11 1 1 1 1 0 1 0 0 0 1 0 0 0 1 0 0 1 1 0 0 0 0 0 0 0 0 1 1 1 1 0 1 0 1 1 1 1 0 67 2sComplement Fixesthenonuniquenessofzeroproblem Addingmixedsignsstilleasy Nocycleoverflow(precomputed) Javasapproach(underthehood) Samefixedlengthk,signconvention,anddefinitionof positivenumbersaswith1scomplement Representnumberswith2(k1)x<2(k1) EG.Javasbyterangesfrom128to+127 L11 68 2sComplement Negatives(slightlyharderthan1scomp.): Compute1scomplement Add1 Summarize:x=x+1. 00010010represents18 11101101+1=11101110represents18. Addtogetherwithoutoverflow:00000000 Q:WhataretherangesofJavas32bitintand64bit long?(AllofJavasintegertypesuse2scomplement) L11 69 2sComplement A: 2) 32bitints:Largestint= 011111.1=2311=2,147,483,647 Smallestint= 100000.0=231=2,147,483,648 2)64bitlongs:Largestlong= 011111.1=2631=9,223,372,036,854,775,807 Smallestint= 100000.0=263= 9,223,372,036,854,775,808 L11 70 2sComplement Addition Additionisthesameasusualbinaryadditionno exceptions!! 11101110=(18)10,11110100=(12)10 Sumtogether(11100010)=(30)10: Carry: x +y 1 1 1 1 1 1 0 1 1 0 1 1 1 0 0 0 L11 71 2sComplement Addition Additionisthesameasusualbinaryadditionno exceptions!! 11101110=(18)10,11110100=(12)10 Sumtogether(11100010)=(30)10: Carry: x +y 1 1 1 1 1 1 0 1 1 0 1 1 1 0 0 0 0 L11 72 2sComplement Additi...

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CS 1571 Introduction to AI Lecture 13Propositional logicMilos Hauskrecht milos@cs.pitt.edu 5329 Sennott SquareCS 1571 Intro to AIM. HauskrechtAnnouncements Homework assignment 5 is out Midterm exam: Wednesday, October 25, 2006 Course web p
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Probabilistic Principal Component Analysis and the E-M algorithmThe Minh Luong CS 3750 October 23, 2007Outline Probabilistic Principal Component Analysis Latent variable models Probabilistic PCA Formulation of PCA model Maximum likelihood est
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CS 441 Discrete Mathematics for CS Lecture 19Summations, CardinalityMilos Hauskrecht milos@cs.pitt.edu 5329 Sennott SquareCS 441 Discrete mathematics for CSM. HauskrechtCourse administration Homework 5 is due today Homework 6 is out Due o
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University of Pittsburgh CS 2740 Knowledge Representation Professor Milos HauskrechtHandout 5 October 1, 2008Problem assignment 4Due: Wednesday, October 8, 2008UnicationThe unication process in FOL aims to nd the most general substitution tha
Pittsburgh - CS - 2740
CS 2740 Knowledge representation Lecture 1Knowledge representationMilos Hauskrecht milos@cs.pitt.edu 5329 Sennott SquareCS 2740 Knowledge representationM. HauskrechtCourse administrationInstructor: Milos Hauskrecht 5329 Sennott Square milo
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CS 3750 Machine Learning Lecture 11Monte Carlo inferenceMilos Hauskrecht milos@cs.pitt.edu 5329 Sennott SquareCS 3750 Advanced Machine LearningMarkov chain Monte Carlo Likelihood weighting: samples are generated according to Q and every sampl
Pittsburgh - CS - 2710
CS 2710 Foundations of AI Lecture 8Adversarial searchMilos Hauskrecht milos@cs.pitt.edu 5329 Sennott SquareCS 2710 Foundations of AIGame search Game-playing programs developed by AI researchers since the beginning of the modern AI era Progr
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CS 1571 Introduction to AI Lecture 12Adversarial searchMilos Hauskrecht milos@cs.pitt.edu 5329 Sennott SquareCS 1571 Intro to AIM. HauskrechtAnnouncements Homework assignment 4 is out Programming and experiments Simulated annealing + Gen
Pittsburgh - MAY - 2005
FEATUREAN EDITOR ON A MISSION BY JESSICA MESMANSO YOU WANT TOCHANGETHE WORLD?HSome people might say Ive reached a point in my life where Im not afraid. But Ive never been afraid, says Catherine DeAngelis.PHOTOGRAPHY |ere comes Dr. De, h
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Pittsburgh - EXP - 1652
Internet WavesDisruptive Technologies&gt; Cool ToolsDigging Digsby and Tweeting Locally&gt; Database ReviewSmart Search Engines Find Best Facts Page 26Page 19Page 41iJune 2008Vol. 25 I Issue 6The Newspaper for Users and Producers of Elect
Pittsburgh - SIS - 793
MARLA MISEKMirror Image InternetThrough the Looking GlassIike the heroine of Lewis Carroll's Alice's Adventures in Wotiderland, who finds herself in a fantastical place where things are not always as they seem, Intemet users generally have no