% BAYES file bayes.m Bayesian reversal of conditional probabilities
% Version of 7/6/93 
% Input P(E|Ai) and P(Ai)
% Calculates P(Ai|E) and P(Ai|Ec)
disp('Requires input PEA = [P(E|A1) P(E|A2) ... P(E|An)]')
disp(' and PA = [P(A1) P(A2) ... P(An)]')
disp('Determines PAE  = [P(A1|E) P(A2|E) ... P(An|E)]')
disp('       and PAEc = [P(A1|Ec) P(A2|Ec) ... P(An|Ec)]')
PEA  = input('Enter matrix PEA of conditional probabilities  ');
PA   = input('Enter matrix  PA of probabilities  ');
PE   = PEA*PA';
PAE  = (PEA.*PA)/PE;
PAEc = ((1 - PEA).*PA)/(1 -  PE);
disp(' ')
disp(['P(E) = ',num2str(PE),])
disp(' ')
disp('    P(E|Ai)   P(Ai)     P(Ai|E)   P(Ai|Ec)')
disp([PEA; PA; PAE; PAEc]')
disp('Various quantities are in the matrices PEA, PA, PAE, PAEc, named above')