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def binom(n, k):
"""Quickly adapted from https://stackoverflow.com/questions/26560726/python-binomial-coefficient"""
if k < 0 or k > n:
return 0
if k == 0 or k == n:
return 1
total_ways = 1
for i in range(min(k, n - k)):
total_ways = total_ways * (n - i) // (i + 1)
return total_ways
def max_confs_cnt(formula=""):
"""Get the maximal number of configurations for a given chemical formula."""
from IsoSpecPy import IsoParamsFromFormula
f = IsoParamsFromFormula(formula)
if f.atomCounts:
N = 1
for n, p in zip(f.atomCounts, f.probs):
N *= binom(n+len(p)-1, n)
return N
else:
return 0
def test_max_confs_cnt():
assert max_confs_cnt("O100") == 5151
assert max_confs_cnt("O100N10S6") == 4759524
test_formulas = [ 'O100',
'O100N10S6',
'C100H202',
'S10H20' ]
def test_all_configs_output_cnt():
"""Test if IsoSpecPy output correctly all configurations."""
from IsoSpecPy import IsoThreshold
global test_formulas
for f in test_formulas:
I = IsoThreshold(formula=f, threshold=0.0, absolute=True)
assert len(I) == max_confs_cnt(f)
print("Seems OK!")
if __name__ == "__main__":
test_all_configs_output_cnt()
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