v4.1:: Added a random number generator for the exponential distribution.
git-svn-id: https://www.dynare.org/svn/dynare/trunk@2417 ac1d8469-bf42-47a9-8791-bf33cf982152time-shift
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function rnd = exprnd(a)
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% Random samples from the exponential distribution with expectation 1/a
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% and variance (1/a)^2.
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%
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% INPUTS
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% a [double] m*n matrix of positive parameters
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%
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% OUTPUT
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% rnd [double] m*n matrix, independent draws from the exponential
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% distribution rnd(j,j) has expectation 1/a(i,j) and
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% variance (1/a(i,j))^2
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%
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% ALGORITHM
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% Inverse transform sampling.
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%
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% SPECIAL REQUIREMENTS
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% None.
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%
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% Copyright (C) 2009 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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if any(a(:)<1e-15)
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disp('exprnd:: The parameter of the exponential distribution has to be positive!')
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error;
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end
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[m,n] = size(a);
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uniform_variates = rand(m,n);
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rnd = -log(uniform_variates)./a;
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