Sign - returns the sign of its argument
integer Sign -1,0, or 1
double Sign -1,0, or 1
The C++ standard library does not define a sign function because
there is no general agreement on the return value for 0. The function
Sign implements the decision made for Mathematica: if the argument is
0, Sign returns 0.
The return value is always an integer
[1] The Mathematica Book "Sign"
Diesmann
2007.11.28
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