[issue8986] math.erfc OverflowError
report at bugs.python.org
Sun Jun 13 11:34:31 CEST 2010
Mark Dickinson <dickinsm at gmail.com> added the comment:
Looking at the source, I think I know where this is coming from: one of the terms in the expression for erfc(x) is exp(-x*x). For abs(x) >= 27.284 or so, this underflows to zero.
So the likely cause is that whatever platform you're on is setting errno to ERANGE on underflow to 0; that errno value later gets interpreted as representing an overflow.
And for x >= 30.0 a constant expression is used instead, so there's no OverflowError any more.
Okay: solved in principle!
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