Generalizing Fibonacci sequeue with SICStus Prolog
- by Christophe Herreman
I'm trying to find a solution for a query on a generalized Fibonacci sequence (GFS). The query is: are there any GFS that have 885 as their 12th number? The initial 2 numbers may be restricted between 1 and 10.
I already found the solution to find the Nth number in a sequence that starts at (1, 1) in which I explicitly define the initial numbers. Here is what I have for this:
fib(1, 1).
fib(2, 1).
fib(N, X) :-
N #> 1,
Nmin1 #= N - 1,
Nmin2 #= N - 2,
fib(Nmin1, Xmin1),
fib(Nmin2, Xmin2),
X #= Xmin1 + Xmin2.
For the query mentioned I thought the following would do the trick, in which I reuse the fib method without defining the initial numbers explicitly since this now needs to be done dynamically:
fib2 :-
X1 in 1..10,
X2 in 1..10,
fib(1, X1),
fib(2, X2),
fib(12, 885).
... but this does not seem to work.
Is it not possible this way to define the initial numbers, or am I doing something terribly wrong? I'm not asking for the solution, but any advice that could help me solve this would be greatly appreciated.
