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yap-6.3/CLPQR/clpqr/examples/monash/mortgage
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/*
**********************************************************************
*
* CLP(R) Version 2.0 (Example Programs Release)
* (C) Copyright, March 1986, Monash University
*
**********************************************************************
*/
%
% Calculate compound interest.
% Arguments are Principal, Time (months), Interest (fraction), Balance,
% and Monthly Payment.
%
% The goals ?- go1 demonstrates
% obtaining ground answers for two different combinations of inputs.
% The goals ?- go2 and ?- go3 deal with getting linear
% equations as answers, while ?- go4 produces a
% polynomial equation.
%
mg(P,T,I,B,MP):-
T > 0,
T <= 1,
B + MP = P * (1 + I).
mg(P,T,I,B,MP):-
T > 1,
mg(P * (1 + I) - MP, T - 1, I, B, MP).
go1:- mg(120000,120,0.01,0,MP), printf("Forward: MP = %g\n",[MP]),
mg(P,120,0.01,0,MP), printf("Backward: P = %g\n",[P]).
% Answer:
% Forward: MP = 1721.651381
% Backward: P = 120000
go2:- mg(P,120,0.01,0,MP), dump([P,MP]).
% Answer:
% 2 ?- go2.
% P = 69.700522*MP
go3:- mg(P,120,0.01,B,MP), dump([P,B,MP]).
% Answer:
% 3 ?- go3.
% P = 0.302995*B + 69.700522*MP
go4:- mg(999, 3, Int, 0, 400), dump.
% Answer:
% 400 = (-400 + (599 + 999*Int) * (1 + Int)) * (1 + Int)
?- printf("\n>>> Sample goals: go1/0, go2/0, go3/0, go4/0\n", []).