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yap-6.3/packages/prism/exs/alarm.psm
2011-11-10 12:24:47 +00:00

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%%%%
%%%% Bayesian networks (1) -- alarm.psm
%%%%
%%%% Copyright (C) 2004,2006,2008
%%%% Sato Laboratory, Dept. of Computer Science,
%%%% Tokyo Institute of Technology
%% This example is borrowed from:
%% Poole, D., Probabilistic Horn abduction and Bayesian networks,
%% In Proc. of Artificial Intelligence 64, pp.81-129, 1993.
%%
%% (Fire) (Tampering)
%% / \ /
%% ((Smoke)) (Alarm)
%% |
%% (Leaving) (( )) -- observable node
%% | ( ) -- hidden node
%% ((Report))
%%
%% In this network, we assume that all rvs (random variables)
%% take on {yes,no} and also assume that only two nodes, `Smoke'
%% and `Report', are observable.
%%-------------------------------------
%% Quick start : sample session
%%
%% ?- prism(alarm),go. % Learn parameters from randomly generated
%% % 100 samples
%%
%% Get the probability and the explanation graph:
%% ?- prob(world(yes,no)).
%% ?- probf(world(yes,no)).
%%
%% Get the most likely explanation and its probability:
%% ?- viterbif(world(yes,no)).
%% ?- viterbi(world(yes,no)).
%%
%% Compute conditional hindsight probabilities:
%% ?- chindsight(world(yes,no)).
%% ?- chindsight_agg(world(yes,no),world(_,_,query,yes,_,no)).
go:- alarm_learn(100).
%%-------------------------------------
%% Declarations:
:- set_prism_flag(data_source,file('world.dat')).
% When we run learn/0, the data are supplied
% from `world.dat'.
values(_,[yes,no]). % We declare multiary random switch msw(.,V)
% used in this program such that V (outcome)
% is one of {yes,no}. Note that '_' is
% an anonymous logical variable in Prolog.
% The distribution of V is specified by
% set_params below.
%%------------------------------------
%% Modeling part:
%%
%% The above BN defines a joint distribution
%% P(Fire,Tapering,Smoke,Alarm,Leaving,Report).
%% We assume `Smoke' and `Report' are observable while others are not.
%% Our modeling simulates random sampling of the BN from top nodes
%% using msws. For each rv, say `Fire', we introduce a corresponding
%% msw, say msw(fi,Fi) such that
%% msw(fi,Fi) <=> sampling msw named fi yields the outcome Fi.
%% Here fi is a constant intended for the name of rv `Fire.'
%%
world(Fi,Ta,Al,Sm,Le,Re) :-
%% Define a distribution for world/5 such that e.g.
%% P(Fire=yes,Tapering=yes,Smoke=no,Alarm=no,Leaving=no,Report=no)
%% = P(world(yes,yes,no,no,no,no))
msw(fi,Fi), % P(Fire)
msw(ta,Ta), % P(Tampering)
msw(sm(Fi),Sm), % CPT P(Smoke | Fire)
msw(al(Fi,Ta),Al), % CPT P(Alarm | Fire,Tampering)
msw(le(Al),Le), % CPT P(Leaving | Alarm)
msw(re(Le),Re). % CPT P(Report | Leaving)
world(Sm,Re):-
%% Define marginal distribution for `Smoke' and `Report'
world(_,_,_,Sm,_,Re).
%%------------------------------------
%% Utility part:
alarm_learn(N) :-
unfix_sw(_), % Make all parameters changeable
set_params, % Set parameters as you specified
get_samples(N,world(_,_),Gs), % Get N samples
fix_sw(fi), % Preserve the parameter values
learn(Gs). % for {msw(fi,yes), msw(fi,no)}
% alarm_learn(N) :-
% %% generate teacher data and write them to `world.dat'
% %% before learn/0 is called.
% write_world(N,'world.dat'),
% learn.
set_params :-
set_sw(fi,[0.1,0.9]),
set_sw(ta,[0.15,0.85]),
set_sw(sm(yes),[0.95,0.05]),
set_sw(sm(no),[0.05,0.95]),
set_sw(al(yes,yes),[0.50,0.50]),
set_sw(al(yes,no),[0.90,0.10]),
set_sw(al(no,yes),[0.85,0.15]),
set_sw(al(no,no),[0.05,0.95]),
set_sw(le(yes),[0.88,0.12]),
set_sw(le(no),[0.01,0.99]),
set_sw(re(yes),[0.75,0.25]),
set_sw(re(no),[0.10,0.90]).
write_world(N,File) :-
get_samples(N,world(_,_),Gs),tell(File),write_world(Gs),told.
write_world([world(Sm,Re)|Gs]) :-
write(world(Sm,Re)),write('.'),nl,write_world(Gs).
write_world([]).