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ncaq/pi.prolog

Last active December 2, 2016 13:59
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2015-07に記述.prologによる格子点の個数からの円周率の近似値の計算
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pi.prolog
piExp(R, Pi) :- dimension(circle, R, Cs), dimension(box, R, Bs), Pi is Cs / Bs.
dimension( box, R, Ps) :- Ps is R * R.
dimension(circle, R, Ps) :- dimensionRec(circle, 0, R, Psr), Ps is Psr * 4.
dimensionRec( _, X, R, Ps) :- X > R, Ps is 0.
dimensionRec(circle, X, R, Ps) :- X =< R, line(circle, X, R, P), dimensionRec(circle, X + 1, R, NP), Ps is P + NP.
line(circle, X, R, P) :- hypot(X, Y, R), P is Y.
hypot(X, Y, R) :- nonvar(X), nonvar(Y), sqrt(X * X + Y * Y, R).
hypot(X, Y, R) :- nonvar(X), nonvar(R), sqrt(R * R - X * X, Y).
hypot(X, Y, R) :- nonvar(Y), nonvar(R), sqrt(R * R - Y * Y, X).
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