60 lines
1.4 KiB
Python
60 lines
1.4 KiB
Python
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from functools import wraps
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def recurrence_memo(initial):
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"""
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Memo decorator for sequences defined by recurrence
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See usage examples e.g. in the specfun/combinatorial module
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"""
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cache = initial
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def decorator(f):
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@wraps(f)
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def g(n):
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L = len(cache)
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if n <= L - 1:
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return cache[n]
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for i in range(L, n + 1):
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cache.append(f(i, cache))
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return cache[-1]
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return g
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return decorator
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def assoc_recurrence_memo(base_seq):
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"""
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Memo decorator for associated sequences defined by recurrence starting from base
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base_seq(n) -- callable to get base sequence elements
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XXX works only for Pn0 = base_seq(0) cases
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XXX works only for m <= n cases
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"""
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cache = []
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def decorator(f):
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@wraps(f)
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def g(n, m):
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L = len(cache)
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if n < L:
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return cache[n][m]
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for i in range(L, n + 1):
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# get base sequence
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F_i0 = base_seq(i)
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F_i_cache = [F_i0]
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cache.append(F_i_cache)
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# XXX only works for m <= n cases
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# generate assoc sequence
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for j in range(1, i + 1):
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F_ij = f(i, j, cache)
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F_i_cache.append(F_ij)
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return cache[n][m]
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return g
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return decorator
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