def sum(iterable, start=None):
"""NGSolve sum function that uses the first element of an iterable as
start argument if no start argument is provided."""
if start is not None:
return builtin_sum(iterable, start)
generator = iter(iterable)
try:
first = next(generator)
except StopIteration:
return 0
return builtin_sum(generator, first)
def sum(x):
return builtin_sum(x)