Programming with CLP($\Re$) (II)

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$\frac{e}{4} = \frac{1}{1} - \frac{1}{2} + \frac{1}{3} - \frac{1}{4} + \cdots$ (converges very slowly)

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CLP($\Re$) program:

is_E(N, E4*4):- is_E(N, 1, 1, E4).

is_E(0, Mult, Sign, 0).
is_E(N, Mult, Sign, Sign/Mult + RestE):-
N > 0,
is_E(N-1, Mult+1, -Sign, RestE).

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The series added up to the 11$^{\rm th}$ term:

?- is_E(11, E).
E = 2.94618

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How many terms needed to achieve a given accuracy?

?- abs(E-E1)<0.01, is_E(N,E), is_E(N+1,E1).
N = 400, E1 = 2.77757, E = 2.76759

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abs(E-E1) < 0.01 is delayed and not evaluated until E and E1 have a known value

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Only an example: can be made much more efficiently