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On 2013-09-05 09:45, Alexandros Drymonitis wrote:
OK, index 0 is the negative of index 2,
no not really, they just happen to be the same.
which can again make sense as it's a sine (supposing that index 0 is a copy of the table's last element), but index 512 doesn't have that value, why? And why do indices 1 and 513 have different values too?
do they?
when it comes to floating point, "equality" becomes a little bit fuzzy. e.g. "0.1" is really the 'same' as "0.100000001490116119384765625" [1].
comparing the values, you can see that they are not *very* wrong:
array[512]-array[0] = -5.30668e-6 = -0.0000053 array[513]-array[1] = -5.30718e-6 = -0.0000053 array[514]-array[2] = -5.30668e-6 = -0.0000053
so the errors are really rather small, and hopefully don't matter so much in the interpolation (which is another approximation anyhow).
the reason why the error is not smaller, is that Pd internally (src/g_array.c:896) deals with a PI value of 3.14159, which is a rather rough estimate and is the reason why the cycle is not exactly 512 points long.
fgamsdr IOhannes
[1] http://en.wikipedia.org/wiki/Floating_point#Representable_numbers.2C_convers...