Why does numpy.power return 0 for small exponents while math.pow returns the correct answer?

In [25]: np.power(10,-100)
Out[25]: 0

In [26]: math.pow(10,-100)
Out[26]: 1e-100

I would expect both the commands to return 1e-100. This is not a precision issue either, since the issue persists even after increasing precision to 500. Is there some setting which I can change to get the correct answer?

Solution 1:

Oh, it's much "worse" than that:

In [2]: numpy.power(10,-1)   
Out[2]: 0

But this is a hint to what's going on: 10 is an integer, and numpy.power doesn't coerce the numbers to floats. But this works:

In [3]: numpy.power(10.,-1)
Out[3]: 0.10000000000000001

In [4]: numpy.power(10.,-100)
Out[4]: 1e-100

Note, however, that the power operator, **, does convert to float:

In [5]: 10**-1
Out[5]: 0.1

Solution 2:

numpy method assumes you want integer returned since you supplied an integer.

np.power(10.0,-100) 

works as you would expect.