Also:
(defn g ^double [^double x] (+ (Math/sin (* 2.3 x)) (Math/cos (* 3.7 x))))
On Wed, Feb 5, 2014 at 2:07 PM, Alex Miller <a...@puredanger.com> wrote:
> Others have answered with many useful bits but I would mention that it
> would possibly make a significant performance difference if you added this
> to your code:
>
> (set! *unchecked-math* true)
>
>
>
> On Wednesday, February 5, 2014 7:17:13 AM UTC-6, Glen Fraser wrote:
>>
>> (sorry if you received an earlier mail from me that was half-formed, I
>> hit send by accident)
>>
>> Hi there, I'm quite new to Clojure, and was trying to do some very simple
>> benchmarking with other languages. I was surprised by the floating-point
>> results I got, which differed (for the same calculation, using doubles)
>> compared to the other languages I tried (including C++, SuperCollider, Lua,
>> Python).
>>
>> My benchmark iteratively runs a function 100M times: g(x) <-- sin(2.3x) +
>> cos(3.7x), starting with x of 0.
>>
>> 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. Note that if you only run the
>> function for about ~110 iterations, you get the same answer in Clojure (or
>> very close), but then it diverges.
>>
>> I assume my confusion is due to my ignorance of Clojure and/or Java's
>> math library. I don't think I'm using 32-bit floats or the "BigDecimal"
>> type (I even explicitly converted to double, but got the same results, and
>> if I evaluate the *type* it tells me *java.lang.Double*, which seems
>> right). Maybe Clojure's answer is "better", but I do find it strange that
>> it's different. Can someone explain this to me?
>>
>> Here are some results:
>>
>> *Clojure: ~23 seconds*
>> (defn g [x] (+ (Math/sin (* 2.3 x)) (Math/cos (* 3.7 x))))
>> (loop [i 100000000 x 0] (if (pos? i) (recur (dec i) (g x)) x))
>> ;; final x: *0.24788989279493556 (???)*
>>
>> *C++ (g++ -O2): ~4 seconds*
>> double g(double x) {
>> return std::sin(2.3*x) + std::cos(3.7*x);
>> }
>> int main() {
>> double x = 0;
>> for (int i = 0; i < 100000000; ++i) {
>> x = g(x);
>> }
>> std::cout << "final x: " << x << std::endl;
>> return 0;
>> }
>> // final x: *0.0541718*
>>
>> *Lua: ~39 seconds*
>> g = function(x)
>> return math.sin(2.3*x) + math.cos(3.7*x)
>> end
>>
>> x = 0; for i = 1, 100000000 do x = g(x) end
>> -- Final x: *0.054171801051906*
>>
>> *Python: ~72 seconds*
>> def g(x):
>> return math.sin(2.3*x) + math.cos(3.7*x)
>>
>> x = 0
>> for i in xrange(100000000):
>> x = g(x)
>>
>> # Final x: *0.05417180105190572*
>>
>> *SClang: ~26 seconds*
>> g = { |x| sin(2.3*x) + cos(3.7*x) };
>> f = { |x| 100000000.do{ x = g.(x) }; x};
>> bench{ f.(0).postln };
>> // final x: *0.054171801051906* (same as C++, Lua, Python; different
>> from Clojure)
>>
>> Thanks,
>> Glen.
>>
>> --
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