Python: OverflowError: math range error

I get a Overflow 开发者_C百科error when i try this calculation, but i cant figure out why.

1-math.exp(-4*1000000*-0.0641515994108)

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The number you're asking math.exp to calculate has, in decimal, over 110,000 digits. That's slightly outside of the range of a double, so it causes an overflow.

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To fix it use:

try:
    ans = math.exp(200000)
except OverflowError:
    ans = float('inf')

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I think the value gets too large to fit into a double in python which is why you get the OverflowError. The largest value I can compute the exp of on my machine in Python is just sligthly larger than 709.78271.

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This may give you a clue why:

http://www.wolframalpha.com/input/?i=math.exp%28-4*1000000*-0.0641515994108%29

Notice the 111442 exponent.

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Unfortunately, no one explained what the real solution was. I solved the problem using:

from mpmath import *

You can find the documentation below:

http://mpmath.org/

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Try np.exp() instead of math.exp()

Numpy handles overflows more gracefully, np.exp(999) results in inf and 1. / (1. + np.exp(999)) therefore simply results in zero

import math 
import numpy as np

print(1-np.exp(-4*1000000*-0.0641515994108))