--On 5 Feb 2014 05:17:13 -0800 Glen Fraser <holag...@gmail.com> wrote:
My benchmark iteratively runs a function 100M times: g(x) <-- sin(2.3x) +
cos(3.7x), starting with x of 0.
A quick look at the series you are computing suggests that it has chaotic
behavior. Another quick looks shows that neither of the two values that
you see after 100M iterations is a fix point. I'd need to do a careful
numerical analysis to be sure, but I suspect that you are computing
a close to random number: any numerical error at some stage is amplified
in the further computation.
If you get identical results from different languages, this suggests that
they all end up using the same numerical code (probably the C math
library). I suggest you try your Python code under Jython, perhaps
that will reproduce the Clojure result by also relying on the JVM
standard library.
In the other languages, I always got the result 0.0541718..., but in
Clojure I get 0.24788989.... I realize this is a contrived case, but --
doing an identical sequence of 64-bit floating-point operations on the
same machine should give the same answer.
Unfortunately not. Your reasoning would be true if everyone adopted
IEEE float operations, but in practice nobody does because the main
objective is speed, not predictability. The Intel hardware is close
to IEEE, but not fully compatible, and it offers some parameters that
libraries can play with to get different results from the same operations.
Konrad.
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