Python rounding error with float numbers -

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this question has answer here:

i don't know if obvious bug, while running python script varying parameters of simulation, realized results delta = 0.29 , delta = 0.58 missing. on investigation, noticed following python code:

for i_delta in range(0, 101, 1):   delta = float(i_delta) / 100    (...)  filename = 'foo' + str(int(delta * 100)) + '.dat'

generated identical files delta = 0.28 , 0.29, same .57 , .58, reason being python returns float(29)/100 0.28999999999999998. isn't systematic error, not in sense happens every integer. created following python script:

import sys  n = int(sys.argv[1])  in range(0, n + 1):   = int(100 * (float(i) / 100))   if != a: print i,

and can't see pattern in numbers rounding error happens. why happen particular numbers?

any number can't built exact powers of 2 can't represented floating point number; needs approximated. closest approximation less actual number.

read what every computer scientist should know floating-point arithmetic.


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