On 2/21/07, Charles R Harris <[EMAIL PROTECTED]> wrote:
On 2/21/07, Robert Kern <[EMAIL PROTECTED]> wrote: > > Christopher Barker wrote: > > 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. <snip> Well, you can always use long double if it is implemented on your > platform. You > will have to construct a value for π yourself, though. I'm afraid that > we don't > really make that easy. > > -- pi = 3. 1415926535 8979323846 2643383279 5028841971 6939937510 5820974944 5923078164 0628620899 8628034825 3421170679 8214808651 *... * I dont know what that looks like when converted to long double. Lessee, In [1]: import numpy In [2]: pi = numpy.float128(3.1415926535897932384626433832795028841971)
I think this is where you go wrong. Your string of digits is first a python float and *then* is converted to a long double. In the intermediate stage it gets truncated and you don't get the precision back. In [3]: numpy.pi - pi
Out[3]: 0.0 In [7]: '%25.20f'%numpy.pi Out[7]: ' 3.14159265358979311600 ' In [8]: '%25.20f'%pi Out[8]: ' 3.14159265358979311600' I think we have a bug. Or else extended arithmetic isn't supported on this machine. Chuck _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
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