Inverse Langevin approach to time-series data analysis by slappypappy128

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									Motivation Parabolic scheme for stochastic inference Summary

Inverse Langevin approach to time-series data analysis
Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto
Universidade de Brasília

Saratoga Springs, MaxEnt 2007

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Outline
1

Motivation Brownian Motion Limit from discrete process Inference about forces/noise Parabolic scheme for stochastic inference Newton’s method Implementation Examples A very naive application to finance

2

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Brownian Motion Limit from discrete process Inference about forces/noise

Outline
1

Motivation Brownian Motion Limit from discrete process Inference about forces/noise Parabolic scheme for stochastic inference Newton’s method Implementation Examples A very naive application to finance

2

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Brownian Motion Limit from discrete process Inference about forces/noise

Classic Brownian motion

Einstein: drunkard walk (Smoluchowski controversy) ) Lots of “Brownian” motions all around: physics, finance, communication etc. Random Gaussian increments (SDE’s — Wanier, Itô) dx = m(x; t) dt + σ(x; t) dB

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Brownian Motion Limit from discrete process Inference about forces/noise

Langevin dynamics

We must retain Newtonian physics:
expand the state dv = a(x, v; t) dt + D(x, v; t) dB dx = v dt rich set of solutions from simple equations: linear, exponential, oscillatory, etc

Similar results (classic Brownian)

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Brownian Motion Limit from discrete process Inference about forces/noise

Outline
1

Motivation Brownian Motion Limit from discrete process Inference about forces/noise Parabolic scheme for stochastic inference Newton’s method Implementation Examples A very naive application to finance

2

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Brownian Motion Limit from discrete process Inference about forces/noise

Limit from discrete process

What we tackle (work in progress)

√ Wanier noise dB = β dt: Fokker-Planck/forward Kolmogorov equation. (Brownian motion) Non-analytic noises, Levy, and others: Kramer-Moyal equation. (gas of rigid spheres)

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Brownian Motion Limit from discrete process Inference about forces/noise

Questions

What the drift and the noise?

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Brownian Motion Limit from discrete process Inference about forces/noise

Questions

What the drift and the noise? Is it Fokker-Planck or Kramer-Moyal?

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Brownian Motion Limit from discrete process Inference about forces/noise

Questions

What the drift and the noise? Is it Fokker-Planck or Kramer-Moyal? Can we compare Fokker-Planck to Kramer-Moyal models?

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Brownian Motion Limit from discrete process Inference about forces/noise

Outline
1

Motivation Brownian Motion Limit from discrete process Inference about forces/noise Parabolic scheme for stochastic inference Newton’s method Implementation Examples A very naive application to finance

2

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Brownian Motion Limit from discrete process Inference about forces/noise

Markov Chain

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Brownian Motion Limit from discrete process Inference about forces/noise

Use Bayes theorem...

Likelihood (µ: measurement noise, w: hidden state, η, θ: parameters of interest) p(η|y) = p(y|η) = 1 p(η)p(y|η) p(y) dw dµ dθ p(η, θ)p(µ)p(y|w, µ)p(w|η, θ)

Similar thing for p(θ|y)

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Newton’s method Implementation Examples A very naive application to finance

Outline
1

Motivation Brownian Motion Limit from discrete process Inference about forces/noise Parabolic scheme for stochastic inference Newton’s method Implementation Examples A very naive application to finance

2

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Newton’s method Implementation Examples A very naive application to finance

Exactly soluble propagators

A Markov process is characterized by its propagator p(w0 , w1 , . . . , wN ) = p(w0 )p(w1 |w0 ) . . . p(wN |wN−1 ) We know analytical (Gaussians!) results only for simplest cases F(x, v; t) = −γv − ω 2 x + a0 m

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Newton’s method Implementation Examples A very naive application to finance

The parabolic method

We don’t know how to integrate every model Newton approximation
The force at a small δt is almost constant (but depends on initial position + parameters) We can calculate the trajectory/propagator Repeat this procedure for the next step

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Newton’s method Implementation Examples A very naive application to finance

Outline
1

Motivation Brownian Motion Limit from discrete process Inference about forces/noise Parabolic scheme for stochastic inference Newton’s method Implementation Examples A very naive application to finance

2

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Newton’s method Implementation Examples A very naive application to finance

Delta function approximation
Conjugate prior for p(µ). At some level approximation for large data sets... dµ p(µ)p(y|w, µ) ∼ δ(y − x) Now we have only Gaussian integrations over velocities. Φ= dv p(y0 , v0 , y1 , v1 , . . . , yN , vN, |θ, η)

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Newton’s method Implementation Examples A very naive application to finance

Main loop
At each integration step, collect a bunch of coefficients η αi − η (ai v2 +2bi vi +2ci vi vi−1 +di v2 +2ei vi−1 +fi ) i−1 e 2 i Gi After each step, some coefficients must be updated before we start with the next integration Φ= η 2 − η f (θ,y) dv p(y, v|θ, η) = e 2 G(θ)
N−1

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Newton’s method Implementation Examples A very naive application to finance

Inference results
Use Laplace approximation to normalize p(θ|y, η), plug-in a Gamma prior p(η) p(θ|y) ∝ p(θ) ¯ G(θ) f (y) + f (θ, y) − f (θ, y) + δ
N+1 +σ+ d 2 2

p(η|y) is calculated analytically

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Newton’s method Implementation Examples A very naive application to finance

Inference results
Use Laplace approximation to normalize p(θ|y, η), plug-in a Gamma prior p(η) p(θ|y) ∝ p(θ) ¯ G(θ) f (y) + f (θ, y) − f (θ, y) + δ
N+1 +σ+ d 2 2

p(η|y) is calculated analytically We use a flat prior p(θ) (I’m ashamed!)

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Newton’s method Implementation Examples A very naive application to finance

Outline
1

Motivation Brownian Motion Limit from discrete process Inference about forces/noise Parabolic scheme for stochastic inference Newton’s method Implementation Examples A very naive application to finance

2

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Newton’s method Implementation Examples A very naive application to finance

Oscillatory brownian motion
Force parameters vs. data length
constant linear quadratic 0.05

0.00

Coefficient

-0.05

-0.10

-0.15

-0.20

103

104

105

Data length

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Newton’s method Implementation Examples A very naive application to finance

Comments

Works pretty well with artificially generated time series Still, it does not get the diffusion coefficient quite right in some cases It is also somewhat robust to the existence of dissipative forces

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Newton’s method Implementation Examples A very naive application to finance

Some results

Simple Harmonic Dissipative D-H

η(1) 0.96(0.03) 0.78(0.03) 1.06(0.03) 1.07(0.03)

θ1 (0) −0.07(0.02) −0.04(0.08) 0.08(0.02) −0.04(0.08)

θ2 (0.1) −9 × 10−7 (5 × 10−4 ) −0.099(0.003) −5 × 10−4 (9 × 10−4 ) −0.096(0.004)

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Newton’s method Implementation Examples A very naive application to finance

Outline
1

Motivation Brownian Motion Limit from discrete process Inference about forces/noise Parabolic scheme for stochastic inference Newton’s method Implementation Examples A very naive application to finance

2

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Newton’s method Implementation Examples A very naive application to finance

You will not win any money!

There is no force. This will NOT make you win money!

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Newton’s method Implementation Examples A very naive application to finance

You will not win any money!

There is no force. This will NOT make you win money! But this is the expected behavior, of course Things to explore (speculation-crash patterns):
noise may not be Wanier volatility time we can introduce trends as a time-dependent force

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Newton’s method Implementation Examples A very naive application to finance

The time series data
GE closing values
1.0 0.5

log2-return

0.0 -0.5 -1.0 -1.5

1970

1980

1990

2000

year

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Summary
Given f (x, θ), it is possible to infer θ and the intensity of the noise which governs a Langevin system

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Summary
Given f (x, θ), it is possible to infer θ and the intensity of the noise which governs a Langevin system Open possibilities: better linear approximations, time-dependent parameters, linear diffusion coefficient.

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Summary
Given f (x, θ), it is possible to infer θ and the intensity of the noise which governs a Langevin system Open possibilities: better linear approximations, time-dependent parameters, linear diffusion coefficient. Open issues
Work out a decent prior p(θ) (and calculate the evidence!)

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Summary
Given f (x, θ), it is possible to infer θ and the intensity of the noise which governs a Langevin system Open possibilities: better linear approximations, time-dependent parameters, linear diffusion coefficient. Open issues
Work out a decent prior p(θ) (and calculate the evidence!) Treatment of noise is not really satisfactory

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis

Motivation Parabolic scheme for stochastic inference Summary

Summary
Given f (x, θ), it is possible to infer θ and the intensity of the noise which governs a Langevin system Open possibilities: better linear approximations, time-dependent parameters, linear diffusion coefficient. Open issues
Work out a decent prior p(θ) (and calculate the evidence!) Treatment of noise is not really satisfactory Dissipative forces (easy) and non-Wanier and Levy noises (potentially very hard)

Fábio Macêdo Mendes Anníbal Dias Figueiredo Neto

Inverse Langevin approach to time-series data analysis


								
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