Hi all,
On 24.07.2014 11:59, Eelco Hoogendoorn wrote:
> np.mean isn't broken; your understanding of floating point number is.
I am quite new to python, and this problem is discussed over and over
for other languages too. However, numpy's summation problem appears with
relatively small arrays already:
py>import numpy as np
py>np.ones((4000,4000), np.float32).mean()
1.0
py>np.ones((5000,5000), np.float32).mean()
0.67108864000000001
A 5000*5000 image is not unusual anymore today.
In IDL:
IDL> mean(fltarr(5000L, 5000L)+1)
1.0000000
IDL> mean(fltarr(7000L, 7000L)+1)
1.0000000
IDL> mean(fltarr(10000L, 10000L)+1)
0.67108864
I can't really explain why there are differences between the two
languages (IDL uses 32-bit, single-precision, floating-point numbers)
Fabien
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