%
% Ex.3 on-line average estimation
%
% Haixun Wang, hxwang@cs.ucla.edu

%%
database( {
	q(P:float, X:integer)
} ).

%%
export appro_avg(P).
export exact_avg(P).
%%
appro_avg(myavg<A>)<-q(P,A).
exact_avg(avg_all<A>)<-q(P,A).

single(myavg, X, (X,0,1)).
multi(myavg, As, (Ao,Go,Co), (A,G,C)) <- 
    C = Co+1,
    A = (Ao*Co*1.0+As)/C,
    if ( 1-Ao/A <0.003, 1-Ao/A>-0.003 then
	G=Go+1
    else
	G=0),
    Go<10.         

return(myavg, X, (A,G,C), (A,C))<-
    mod(C,10).
return(myavg, nil, (A,G,C), (A,C)).

mod(X,X).
mod(X,Y)<-X>Y, mod(X-Y,Y).