function [p1,p2,prior]=pp_prior(dat,type)

%

% PP_PRIOR Construction of prior for two proportions using discrete models.

%	[P1,P2,PRIOR]=PP_PRIOR(DAT,TYPE) returns vectors P1 and P2 of values

%	of two proportions and a matrix PRIOR of probabilities, where DAT

%	is a vector containing the smallest, largest and grid size for each

%	proportion, and TYPE indicates the type of prior ('u' for uniform prior

%	't' for testing prior which assigns a probability of .5 to P1=P2).



if nargin==1, type='u'; end



n=dat(3);

p1=linspace(dat(1),dat(2),dat(3));

p2=p1;

[P1,P2]=meshgrid(p1,p2);     

if type=='u'

  prior=1/n^2*ones(n,n);

elseif type=='t'

  prior=.5/n*(P1==P2)+.5/(n^2-n)*(P1~=P2);

end

  







