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multinomial coefficient iterator This routine has been optimized for `m` large with respect to `n` by taking advantage of the fact that when the monomial tuples `t` are stripped of zeros, their coefficient is the same as that of the monomial tuples from ``multinomial_coefficients(n, n)``. Therefore, the latter coefficients are precomputed to save memory and time. >>> from sympy.ntheory.multinomial import multinomial_coefficients >>> m53, m33 = multinomial_coefficients(5,3), multinomial_coefficients(3,3)(more...)

def multinomial_coefficients_iterator(m, n, _tuple=tuple): """multinomial coefficient iterator This routine has been optimized for `m` large with respect to `n` by taking advantage of the fact that when the monomial tuples `t` are stripped of zeros, their coefficient is the same as that of the monomial tuples from ``multinomial_coefficients(n, n)``. Therefore, the latter coefficients are precomputed to save memory and time. >>> from sympy.ntheory.multinomial import multinomial_coefficients >>> m53, m33 = multinomial_coefficients(5,3), multinomial_coefficients(3,3) >>> m53[(0,0,0,1,2)] == m53[(0,0,1,0,2)] == m53[(1,0,2,0,0)] == m33[(0,1,2)] True Examples ======== >>> from sympy.ntheory.multinomial import multinomial_coefficients_iterator >>> it = multinomial_coefficients_iterator(20,3) >>> next(it) ((3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0), 1) """ if m < 2*n or n == 1: mc = multinomial_coefficients(m, n) for k, v in mc.items(): yield(k, v) else: mc = multinomial_coefficients(n, n) mc1 = {} for k, v in mc.items(): mc1[_tuple(filter(None, k))] = v mc = mc1 t = [n] + [0] * (m - 1) t1 = _tuple(t) b = _tuple(filter(None, t1)) yield (t1, mc[b]) if n: j = 0 # j will be the leftmost nonzero position else: j = m # enumerate tuples in co-lex order while j < m - 1: # compute next tuple tj = t[j] if j: t[j] = 0 t[0] = tj if tj > 1: t[j + 1] += 1 j = 0 else: j += 1 t[j] += 1 t[0] -= 1 t1 = _tuple(t) b = _tuple(filter(None, t1)) yield (t1, mc[b])

**sympy**(Download)

from sympy.utilities.pytest import raises from sympy.utilities.iterables import capture from sympy.ntheory.multinomial import multinomial_coefficients_iterator

(1, 0, 2): 3, (0, 2, 1): 3, (0, 1, 2): 3, (3, 0, 0): 1, (2, 0, 1): 3, (1, 2, 0): 3, (1, 1, 1): 6, (0, 0, 3): 1} assert dict(multinomial_coefficients_iterator(2, 0)) == {(0, 0): 1} assert dict( multinomial_coefficients_iterator(2, 1)) == {(0, 1): 1, (1, 0): 1} assert dict(multinomial_coefficients_iterator(2, 2)) == \ {(2, 0): 1, (0, 2): 1, (1, 1): 2} assert dict(multinomial_coefficients_iterator(3, 3)) == mc

src/s/y/sympy-0.7.5/sympy/ntheory/tests/test_ntheory.py

**sympy**(Download)

from sympy.utilities.pytest import raises from sympy.utilities.iterables import capture from sympy.ntheory.multinomial import multinomial_coefficients_iterator

(1, 0, 2): 3, (0, 2, 1): 3, (0, 1, 2): 3, (3, 0, 0): 1, (2, 0, 1): 3, (1, 2, 0): 3, (1, 1, 1): 6, (0, 0, 3): 1} assert dict(multinomial_coefficients_iterator(2, 0)) == {(0, 0): 1} assert dict( multinomial_coefficients_iterator(2, 1)) == {(0, 1): 1, (1, 0): 1} assert dict(multinomial_coefficients_iterator(2, 2)) == \ {(2, 0): 1, (0, 2): 1, (1, 1): 2} assert dict(multinomial_coefficients_iterator(3, 3)) == mc