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

David Goldsmith David.L.Goldsmith@noaa....
Wed Feb 21 13:52:39 CST 2007


Anne Archibald wrote:
> On 21/02/07, Zachary Pincus <zpincus@stanford.edu> wrote:
>
>   
>> A corrolary: in general do not two floating-point values for equality
>> -- use something like numpy.allclose. (Exception -- equality is
>> expected if the exact sequence of operations to generate two numbers
>> were identical.)
>>     
>
> I really can't agree that blindly using allclose() is a good idea. For
> example, allclose(plancks_constant,0) and the difference leads to
> quantum mechanics... you really have to know how much difference you
> expect and how big your numbers are going to be.
>
> Anne
>   
"Precisely!" ;-)

Last time we had a posting like this, didn't one of the respondents 
include a link to something within the numpy Web docs that talks about 
floating point precision?

DG
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