# LinReg: Simple Linear Regression In RcppSMC: Rcpp Bindings for Sequential Monte Carlo

## Description

A simple example based on estimating the parameters of a linear regression model using

* Data annealing sequential Monte Carlo (LinReg).

* Likelihood annealing sequential Monte Carlo (LinRegLA).

* Likelihood annealing sequential Monte Carlo with the temperature schedule, number of MCMC repeats and random walk covariance matrices adapted online (LinRegLA_adapt).

## Usage

 1 2 3 4 5 LinReg(model, particles = 1000, plot = FALSE) LinRegLA(model, particles = 1000, temperatures = seq(0, 1, 0.05)^5) LinRegLA_adapt(model, particles = 1000, resampTol = 0.5, tempTol = 0.9) 

## Arguments

 model Choice of regression model (1 for density as the predictor and 2 for adjusted density as the predictor). particles An integer specifying the number of particles. plot A boolean variable to determine whether to plot the posterior estimates. temperatures In likelihood annealing SMC the targets are defined as P(y|θ)^{γ_t}P(θ) where 0=γ_0≤ … ≤ γ_T = 1 can be referred to as the temperatures, P(y|θ) is the likelihood and P(θ) is the prior. resampTol The adaptive implementation of likelihood annealing SMC allows for the resampling tolerance to be specified. This parameter can be set to a value in the range [0,1) corresponding to a fraction of the size of the particle set or it may be set to an integer corresponding to an actual effective sample size. tempTol A tolerance for adaptive choice of the temperature schedule such that the conditional ESS is maintained at tempTol*particles.

## Details

Williams (1959) considers two competing linear regression models for the maximum compression strength parallel to the grain for radiata pine. Both models are of the form

y_i = α + β (x_i - \bar{x}) + ε_i,

where ε_i ~ N(0,σ^2) and i=1,…,42. Here y is the maximum compression strength in pounds per square inch. The density (in pounds per cubic foot) of the radiata pine is considered a useful predictor, so model 1 uses density for x. Model 2 instead considers the density adjusted for resin content, which is associated with high density but not with strength.

This example is frequently used as a test problem in model choice (see for example Carlin and Chib (1995) and Friel and Pettitt (2008)). We use the standard uninformative normal and inverse gamma priors for this example along with the transformation φ=log(σ^2) so that all parameters are on the real line and θ = [α,β,φ]. The evidence can be computed using numerical estimation for both of the competing models. The log evidence is -309.9 for model 1 and -301.4 for model 2.

The LinReg function implements a data annealing approach to this example.

The LinRegLA function implements a likelihood annealing approach to this example.

The LinRegLA_adapt function implements a likelihood annealing approach to this example with adaptation of the temperature schedule, number of MCMC repeats and random walk covariance matrices.

## Value

The LinReg function returns a list containing the final particle approximation to the target (θ and the corresponding weights) as well as the logarithm of the estimated model evidence.

The LinRegLA function returns a list containing the population of particles and their associates log likelihoods, log priors and weights at each iteration. The effective sample size at each of the iterations and several different estimates of the logarithm of the model evidence are also returned.

The LinRegLA_adapt function returns a list containing all of the same output as LinRegLA, in addition to the adaptively chosen temperature schedule and number of MCMC repeats.

## Author(s)

Adam M. Johansen, Dirk Eddelbuettel and Leah F. South

## References

B. P. Carlin and S. Chib. Bayesian model choice via Markov chain Monte Carlo. Journal of the Royal Statistical Society: Series B (Statistical Methodology). 57(3):473-484, 1995.

N. Friel and A. N. Pettitt. Marginal likelihood estimation via power posteriors. Journal of the Royal Statistical Society: Series B (Statistical Methodology). 70(3):589-607, 2008.

Williams, E. (1959). Regression analysis. Wiley.

## Examples

 1 2 3 4 5 res <- LinReg(model=1, particles=1000, plot=TRUE) res <- LinRegLA(model=1, particles=1000) res <- LinRegLA_adapt(model=1, particles=1000) 

RcppSMC documentation built on March 19, 2018, 1:05 a.m.