1. Princeton University AIChE Centennial – CAST – Philadelphia, 2008 I.G. Kevrekidis -C. W. Gear, D. Maroudas, R. Coifman and several other good people- Department of Chemical Engineering, PACM & Mathematics Princeton University, Princeton, NJ 08544 NO EQUATIONS, NO VARIABLES: An engineering approach to complex systems modeling Or Why I fell in love with Newton-Raphson

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4. George Stephanopoulos Kyriakos Zygourakis Christos Takoudis Vassilis Matzouranis Christos Georgakis

5. Princeton University Rutherford Aris Lanny Schmidt Richard McGehee Don Aronson Daniel Joseph L.E. “Skip” Scriven

6. Princeton University Two ways of taking a model f(x)=0 to the computer t x xoxo toto x=x* simulation f(x) x x (0) x (1) x (2) f(x*)=0 x (0) →x (1) →x (2) →…→x* same x* algorithm dynamics: unphysical result (x*): meaningful feedback:design of new trial Extra Bonus: Stability, bifurcation, etc simulation of computer aided analysis

7. Princeton University Basil Nicolaenko (Nichols)Ciprian FoiasJames M. Hyman

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11. “simple”“complicated”“complex” J. Ottino, NWU

12. Princeton University 0 1 No news – drift to Center SELL BUY Neutral Bullish Bearish Bad News Arrives jump left -  - Good News Arrives jump right  + Bad News arrival rate (Poisson) Good News arrival rate (Poisson) If moves to extreme right agent buys and becomes neutral If moves to extreme left agent sells and becomes neutral Sell rate increases bad news arrival rate Buy rate increases good news arrival rate Influence of other investors Buy rate Sell rate - or lemmings falling off a cliff

13. Princeton University SIMULATION RESULTS 50000 agents, ε + =0.075, ε - = - 0.072, v 0 + =v 0 - =20 Open loop response, g = 42

14. Princeton University SIMULATION RESULTS 50000 agents, ε + =0.075, ε - =-0.072, v 0 + = v 0 - =20 Open loop response, g = 46.5

15. Princeton University Multiscale / Complex System Modeling “Textbook” engineering modeling: macroscopic behavior through macroscopic models (e.g. conservation equations augmented by closures) Alternative (and increasingly frequent) modeling situation: Models –at a FINE / ATOMISTIC / STOCHASTIC level – MD, KMC, BD, LB (also CPMD…) Desired Behavior –At a COARSER, Macroscopic Level – E.g. Conservation equations, flow, reaction-diffusion, elasticity Seek a bridge –Between Microscopic/Stochastic Simulation –And “Traditional, Continuum” Numerical Analysis –When closed macroscopic equations are not available in closed form

16. Princeton University What I told you: Solve the equations WITHOUT writing them down. Write “software wrappers” around “fine level” microscopic codes Top level: all algorithms we know and love Bottom level: MD, kMC, LB, BD, heterogeneous/ discrete media, CPMD, hybrid INTERFACE: Trade Function/Jacobian Evaluation for “on demand” experimentation and estimation “Equation Free” (motivated by “matrix free iterative linear algebra”) “Variable Free” (use of diffusion maps to discover good reduction coordinates) Think of the microscopic simulator AS AN EXPERIMENT That you can set up and run at will

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18. Descriptions 1.Detailed: v i for each variables 2.Moments Zeroth moment: density ρ First moment: momentum ρv Second moment Third Moment m3m3 m2m2 m1m1 m0m0 …………. DISTRIBUTIONS & MOMENTS v p(v)

19. Princeton University