Hi, On Wed, Oct 2, 2013 at 6:00 PM, Dave Cook <daverz@gmail.com> wrote:

Can someone explain what is going on here?

In [153]:

small = ones(1, dtype='float32')

In [154]:

small

Out[154]:

array([ 1.], dtype=float32)

In [155]:

small*1e-45

Out[155]:

array([ 1.40129846e-45], dtype=float32)

In [156]:

small*1e-46

Out[156]:

array([ 0.], dtype=float32)

I would expect float32 to be able to represent numbers with exponents as small as -127.

Is it possible you are thinking of 2**-126 rather than 10**-126? In [3]: print np.finfo(np.float32) Machine parameters for float32 --------------------------------------------------------------------- precision= 6 resolution= 1.0000000e-06 machep= -23 eps= 1.1920929e-07 negep = -24 epsneg= 5.9604645e-08 minexp= -126 tiny= 1.1754944e-38 maxexp= 128 max= 3.4028235e+38 nexp = 8 min= -max --------------------------------------------------------------------- In [4]: 2**-126 Out[4]: 1.1754943508222875e-38 So I think your 10**-45 was already 'subnormal' and then 10**-46 went down to 0... Cheers, Matthew