[Numpy-discussion] what goes wrong with cos(), sin()

David Goldsmith David.L.Goldsmith@noaa....
Wed Feb 21 14:27:02 CST 2007

Robert Kern wrote:
> Christopher Barker wrote:
>> I wonder if there are any C math libs that do a better job than you'd 
>> expect from standard FP? (short of unlimited precision ones)
> With respect to π and the zeros of sin() and cos()? Not really. If
> numpy.sin(numpy.pi) were to give you 0.0, it would be *wrong*. numpy.sin() is
> supposed to give you the most accurate result representable in double-precision
> for the input you gave it. numpy.pi is not π.
True, but since the string literal "numpy.pi" is not the same as the 
string literal "3.1415926535897931" there's no reason in principle why 
"numpy.py" couldn't symbolically represent the exact value; of course, 
since numpy does not otherwise support symbolic computation, such an 
adoption would be frivolous and rather silly (but then the Pythons were 
never afraid of being silly). :-)


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