on floating-point numbers
Greg Ewing
greg.ewing at canterbury.ac.nz
Sat Sep 4 11:38:55 EDT 2021
On 5/09/21 2:42 am, Hope Rouselle wrote:
> Here's what I did on this case. The REPL is telling me that
>
> 7.23 = 2035064081618043/281474976710656
If 7.23 were exactly representable, you would have got
723/1000.
Contrast this with something that *is* exactly representable:
>>> 7.875.as_integer_ratio()
(63, 8)
and observe that 7875/1000 == 63/8:
>>> from fractions import Fraction
>>> Fraction(7875,1000)
Fraction(63, 8)
In general, to find out whether a decimal number is exactly
representable in binary, represent it as a ratio of integers
where the denominator is a power of 10, reduce that to lowest
terms, and compare with the result of as_integer_ratio().
--
Greg
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