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Introduction
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Coarse graining Alice and Dinah
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Coarse graining part I - Clustering algorithms
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Coarse graining part II - Entropy
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Markov Chains
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Mathematics of coarse grained Markov chains
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Mathematics of Coarse grained Markov Chains: The General Case
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A puzzle: origin of the slippy counter
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Where we are so far
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Cellular Automata: Introduction
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Israeli and Goldenfeld; projection and commuting diagrams
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Networks of Renormalization
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Fixing a projection: From CA’s to Ising
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Introduction to the Ising Model
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Coarse-graining the Lattice
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Inducing Quartets & Commutation Failure
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Finding Fixed Points
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Ising Model Simulations
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Poking the Creature: An Introduction to Group Theory
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Irreversible Computations, Forgetful Computers and the Krohn-Rhodes Theorem
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From Quantum Electrodynamics to Plasma Physics
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The Thermal Physics of Plasma
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How does a particle move the plasma?
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Charge Renormalization and Feedback
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Conclusion: Keeping the things that matter
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1.1 Introduction » Quiz Solution
Which of these could be a variable in a "macroeconomic" theory of Northern California?
A. the employment history of the most recent hire to Google Research
B. total unemployment in Oakland, California
C. the balance-sheet of a drycleaner's in Palo Alto
D. the total biomass of all the Ph.D. candidates in the Stanford Computer Science department
Answer: (B). (C) is clearly a "microeconomic" variable. A single drycleaner is both part of the economy, and affected by economic facts, but it's hard to see how the many fine-grained details it captures could be relevant to a coarse-grained theory. (A) is a little better, if only because it might tell us about the strategies of a major employer in the region -- but, again, many of the specific details of that most recent hire's life, fascinating as they are, are not likely to have much relevance to the economy as a whole. (D) is more of a summary than (A) and (C), so could play a role in a coarse-grained theory. But it's not a particularly good one: if everyone at Stanford CS doubled their pizza consumption, it would have an effect on the variable, but much less on variables of interest to an economist like inflation.