96 lines
4.1 KiB
Matlab
96 lines
4.1 KiB
Matlab
function [LIK, lik] = univariate_kalman_filter(T,R,Q,H,P,Y,start,mf,kalman_tol,riccati_tol,data_index,number_of_observations,no_more_missing_observations)
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% Computes the likelihood of a stationnary state space model (univariate approach).
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%
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% INPUTS
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% T [double] mm*mm transition matrix of the state equation.
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% R [double] mm*rr matrix, mapping structural innovations to state variables.
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% Q [double] rr*rr covariance matrix of the structural innovations.
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% H [double] pp*1 (zeros(pp,1) if no measurement errors) variances of the measurement errors.
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% P [double] mm*mm variance-covariance matrix with stationary variables
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% Y [double] pp*smpl matrix of (detrended) data, where pp is the maximum number of observed variables.
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% start [integer] scalar, likelihood evaluation starts at 'start'.
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% mf [integer] pp*1 vector of indices.
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% kalman_tol [double] scalar, tolerance parameter (rcond).
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% riccati_tol [double] scalar, tolerance parameter (riccati iteration).
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% data_index [cell] 1*smpl cell of column vectors of indices.
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% number_of_observations [integer] scalar.
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% no_more_missing_observations [integer] scalar.
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%
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% OUTPUTS
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% LIK [double] scalar, likelihood
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% lik [double] vector, density of observations in each period.
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%
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% REFERENCES
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% See "Filtering and Smoothing of State Vector for Diffuse State Space
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% Models", S.J. Koopman and J. Durbin (2003, in Journal of Time Series
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% Analysis, vol. 24(1), pp. 85-98).
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%
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% NOTES
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% The vector "lik" is used to evaluate the jacobian of the likelihood.
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% Copyright (C) 2004-2008 Dynare Team
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%
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% This file is part of Dynare.
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%
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% Dynare is free software: you can redistribute it and/or modify
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% it under the terms of the GNU General Public License as published by
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% the Free Software Foundation, either version 3 of the License, or
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% (at your option) any later version.
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%
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% Dynare is distributed in the hope that it will be useful,
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% but WITHOUT ANY WARRANTY; without even the implied warranty of
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% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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% GNU General Public License for more details.
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%
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% You should have received a copy of the GNU General Public License
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% along with Dynare. If not, see <http://www.gnu.org/licenses/>.
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pp = size(Y,1); % Number of observed variables
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mm = size(T,1); % Number of variables in the state vector.
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smpl = size(Y,2); % Number of periods in the dataset.
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a = zeros(mm,1); % Initial condition of the state vector.
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QQ = R*Q*transpose(R);
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t = 0;
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lik = zeros(smpl+1,1);
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lik(smpl+1) = number_of_observations*log(2*pi); % the constant of minus two times the log-likelihood
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notsteady = 1;
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while notsteady && t<smpl
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t = t+1;
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MF = mf(data_index{t});
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oldP = P;
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for i=1:length(MF)
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prediction_error = Y(data_index{t}(i),t) - a(MF(i));
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Fi = P(MF(i),MF(i)) + H(data_index{t}(i));
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if Fi > kalman_tol
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Ki = P(:,MF(i))/Fi;
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a = a + Ki*prediction_error;
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P = P - (Fi*Ki)*transpose(Ki);
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lik(t) = lik(t) + log(Fi) + prediction_error*prediction_error/Fi;
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end
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end
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a = T*a;
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P = T*P*transpose(T) + QQ;
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if t>no_more_missing_observations
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notsteady = max(max(abs(P-oldP)))>riccati_tol;
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end
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end
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% Steady state kalman filter.
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while t < smpl
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PP = P;
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t = t+1;
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for i=1:pp
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prediction_error = Y(i,t) - a(mf(i));
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Fi = PP(mf(i),mf(i)) + H(i);
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if Fi > kalman_tol
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Ki = PP(:,mf(i))/Fi;
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a = a + Ki*prediction_error;
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PP = PP - (Fi*Ki)*transpose(Ki);
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lik(t) = lik(t) + log(Fi) + prediction_error*prediction_error/Fi;
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end
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end
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a = T*a;
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end
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LIK = .5*(sum(lik(start:end))-(start-1)*lik(smpl+1)/smpl); |