Mauch MIREX 2010

function CPD = noisyor_CPD(bnet, self, leak_inhibit, inhibit)

% NOISYOR_CPD Make a noisy-or CPD

% CPD = NOISYOR_CPD(BNET, NODE_NUM, LEAK_INHIBIT, INHIBIT)

%

% A noisy-or node turns on if any of its parents are on, provided they are not inhibited.

% The prob. that the i'th parent gets inhibited (flipped from 1 to 0) is inhibit(i).

% The prob that the leak node (a dummy parent that is always on) gets inhibit is leak_inhibit.

% These params default to random values if omitted.

%

% Example: suppose C has parents A and B, and the

% link of A->C fails with prob pA and the link B->C fails with pB.

% Then the noisy-OR gate defines the following distribution

%

%  A  B  P(C=0)

%  0  0  1.0

%  1  0  pA

%  0  1  pB

%  1  1  pA * PB

%

% Currently, learning is not supported for noisy-or nodes

% (since the M step is somewhat complicated).

%

% For simple generalizations of the noisy-OR model, see e.g.,

% - Srinivas, "A generalization of the noisy-OR model", UAI 93

% - Meek and Heckerman, "Learning Causal interaction models", UAI 97.

if nargin==0

  % This occurs if we are trying to load an object from a file.

  CPD = init_fields;

  CPD = class(CPD, 'noisyor_CPD', discrete_CPD(1, []));

  return;

elseif isa(bnet, 'noisyor_CPD')

  % This might occur if we are copying an object.

  CPD = bnet;

  return;

end

CPD = init_fields;

ps = parents(bnet.dag, self);

fam = [ps self];

ns = bnet.node_sizes;

assert(all(ns(fam)==2));

assert(isempty(myintersect(fam, bnet.cnodes)));

if nargin < 3, leak_inhibit = rand(1, 1); end

if nargin < 4, inhibit = rand(1, length(ps)); end

CPD.self = self;

CPD.inhibit = inhibit;

CPD.leak_inhibit = leak_inhibit;

% For BIC

CPD.nparams = 0;

CPD.nsamples = 0;

CPD.CPT = []; % cached copy, to speed up CPD_to_CPT

clamped = 1;

CPD = class(CPD, 'noisyor_CPD', discrete_CPD(clamped, ns([ps self])));

%%%%%%%%%%%

function CPD = init_fields()

% This ensures we define the fields in the same order 

% no matter whether we load an object from a file,

% or create it from scratch. (Matlab requires this.)

CPD.self = [];

CPD.inhibit = [];

CPD.leak_inhibit = [];

CPD.nparams = [];

CPD.nsamples = [];

CPD.CPT = [];