I am new to programming. In my latest Python 2.7 project I encountered the following:
RuntimeWarning: overflow encountered in long_scalars
Could someone please elaborate what this means and what I could do to fix that?
The code runs through, but I'm not sure if it is a good idea to just ignore the warning.
It happens during an append process like:
SomeList.append(VeryLongFormula) Here's an example which issues the same warning:
import numpy as np np.seterr(all='warn') A = np.array([10]) a=A[-1] a**a yields
RuntimeWarning: overflow encountered in long_scalars In the example above it happens because a is of dtype int32, and the maximim value storable in an int32 is 2**31-1. Since 10**10 > 2**32-1, the exponentiation results in a number that is bigger than that which can be stored in an int32.
Note that you can not rely on np.seterr(all='warn') to catch all overflow errors in numpy. For example, on 32-bit NumPy
>>> np.multiply.reduce(np.arange(21)+1) -1195114496 while on 64-bit NumPy:
>>> np.multiply.reduce(np.arange(21)+1) -4249290049419214848 Both fail without any warning, although it is also due to an overflow error. The correct answer is that 21! equals
In [47]: import math In [48]: math.factorial(21) Out[50]: 51090942171709440000L According to numpy developer, Robert Kern,
Unlike true floating point errors (where the hardware FPU sets a flag whenever it does an atomic operation that overflows), we need to implement the integer overflow detection ourselves. We do it on the scalars, but not arrays because it would be too slow to implement for every atomic operation on arrays.
So the burden is on you to choose appropriate dtypes so that no operation overflows.
An easy way to overcome this problem is to use 64 bit type
list = numpy.array(list, dtype=numpy.float64)