alanturing: acenturyofcomputingusers.metu.edu.tr/bozsahin/turing-metu-econ.pdf · alanturing:...
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Alan Turing:A Century of Computing
Cem Bozşahin
Cognitive Science Department, The Informatics Institute, METU
www.ii.metu.edu.tr
Department of Economics Seminars, METU
28.5.2012
Bozşahin Alan Turing Centenary
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Alan Mathison Turing: 1912–1954
Bozşahin Alan Turing Centenary 2/23
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What was Turing up to?
He tried just about everything
ChemistryCryptology (Enigma)Bio-genetics (morphogenesis)Abstract computing (algorithms)Applied computing (programming)Mind-body problem (round-the-house chess)Turing testArtificial lifeFoundations of mathematicsArtificial IntelligenceMarathon
Bozşahin Alan Turing Centenary 3/23
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AMT the athlete
Bozşahin Alan Turing Centenary 4/23
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Perhaps the right question is:
How was Turing trying to do everything he did?
Bozşahin Alan Turing Centenary 5/23
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Mark I, 1948. Manchester’s Ferranti Bros.
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Mark I, 2011
Bozşahin Alan Turing Centenary 7/23
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Turing Machine
. . . b b a a a a . . . Input/Output Tape
q0q1
q2
q3 . . .
qn
Finite Control
q1
Reading and Writing Head(moves in both directions)
Bozşahin Alan Turing Centenary 8/23
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A TM
aL L LI
#
#L #
aR # L
#R
#
R
a
I#Ra
#I
IR L#
a
#
a
a
a
#
# aaR #CaL #
not I
‘#’
x
L
R
L
R
find first x on left
x
x
find first x on right
move right
move left
write x
blank
#
A Turing machine to compute f(n,m)=n x m
It copies the second string a number of times given by the first string.
From Lewis and Papadimitriou (1981).
Representation: maps #I #I #m n
to aI aI m n
first__ __
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k-tape TM
1
2
k
FSM
Bozşahin Alan Turing Centenary 10/23
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Putnam-Gold TM
1
2
3
FSM
TM
deneme
E E H
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Non-Turing extensions to Computing
Analog devices (where everything represents itself)Quantum computing
Bankers bewareNew measures of complexity
Bozşahin Alan Turing Centenary 12/23
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What is essential to Turing?
P-G machine is a TMThe nature of relation between representation and computing.Complexity is defined over representation rather than physicaltime and space.One more move of a TM makes the solution one step moreinvolved.
Bozşahin Alan Turing Centenary 13/23
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TM
. . . b b a a a a . . . Input/Output Tape
q0q1
q2
q3 . . .
qn
Finite Control
q1
Reading and Writing Head(moves in both directions)
Bozşahin Alan Turing Centenary 14/23
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k-TTM
1
2
k
FSM
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Problems
Formulable but unsolvable problems
diagonal(X):a: if halt(X,X) goto a otherwise halt.
diagonal(diagonal) ?
Expressible but unformulable problems
What is the next number after π?
The difference is TM representability.
Bozşahin Alan Turing Centenary 16/23
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Foundations of Math and AMT
Turing’s universal combinatorUfg = g(ffg)
U = (λxλy .y(xxy))(λxλy .y(xxy))
Uf = [ (λxλy .y(xxy))(λxλy .y(xxy)) ] f[λy .y([ λx1λy1.y1(x1x1y1) ] [ λx2λy2.y2(x2x2y2) ] y) ] ff ([ λx1λy1.y1(x1x1y1) ] [ λx2λy2.y2(x2x2y2) ] f )f (Uf )
Uf = f (Uf )
Recursion without names, programs without variables!
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Turing Test
(Ann Witbrock; Copeland, B.J., Artificial Intelligence BlackwellPublishers, Oxford, 1993.)
Bozşahin Alan Turing Centenary 18/23
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Searle and Turing
Bozşahin Alan Turing Centenary 19/23
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Programming and Searle
ConceptualIntentional System
ArticulatoryPerceptual System
Person
Performance System
PhonologicalForm
LogicalForm
Grammar
Lexicon(meaning bearing items)
(meaning bearing phrases)
Virtual Machine
Interpretive systemTransductive system
Computer
I/O CPU
Alphabet (finite vocabulary)
Well−formed
programs
(source code)
meaningful
computation
(interp. code)
Grammar
Lexicon(finitely characterizable tokens)
(finitely characterizable sentences)
Bozşahin Alan Turing Centenary 20/23
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does it look like a TM?AMT: intelligent behavior can arise from manipulation ofrepresentation.With representations, we can build models. Without them wetalk about them.Turing representability is the key to Turing’s computing.
Bozşahin Alan Turing Centenary 21/23
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AMT @ 13
“I always seem to want to make things from the thing that iscommonest in nature.”
Bozşahin Alan Turing Centenary 22/23
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AMT @ 9
Bozşahin Alan Turing Centenary 23/23