Re: Impact of implicit arrays...

From	"Chris M. Thomasson" <nospam@nospam.com>
Newsgroups	comp.lang.javascript
Subject	Re: Impact of implicit arrays...
Date	2016-06-14 17:17 -0700
Organization	Aioe.org NNTP Server
Message-ID	<njq6qn$qc3$1@gioia.aioe.org> (permalink)
References	<njhj52$hl3$1@gioia.aioe.org> <4a1c28ea-447b-4e9b-9c75-68ef85c379e7@googlegroups.com>

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> "Michael Haufe (TNO)"  wrote in message
> news:4a1c28ea-447b-4e9b-9c75-68ef85c379e7@googlegroups.com...

>> On Saturday, June 11, 2016 at 12:52:43 PM UTC-5, Chris M. Thomasson 
>> wrote:
>> I created a little complex number library for some new
>> fractal encryption techniques I am going to put online.
>> I am a bit worried about all of the arrays I am using in
>> the following code:
>> ______________________________
>> "use strict";
[...]
>> function ct_complex_mul(c0, c1)
>> {
>>     return [c0[0] * c1[0] - c0[1] * c1[1],
>>             c0[0] * c1[1] + c0[1] * c1[0]];
>> }
[...]
>> function ct_complex_pow(c, p)
>> {
>>     var l = ct_complex_abs(c);
>>     var s = Math.pow(l, p);
>>     var a = Math.atan2(c[1], c[0]) * p;
>>
>>     return [Math.cos(a) * s, Math.sin(a) * s];
>> }
>>
>> function ct_complex_roots(c, p)
>> {
>>     var l = ct_complex_abs(c);
>>     var s = Math.pow(l, 1.0 / p);
>>     var a = Math.atan2(c[1], c[0]) / p;
>>
>>     var n = Math.ceil(Math.abs(p));
>>     var as = (Math.PI * 2) / p;
>>     var roots = [];
>>
>>     for (var i = 0; i < n; ++i)
>>     {
>>         roots.push([Math.cos(a + as * i) * s,
>>                     Math.sin(a + as * i) * s]);
>>     }
>>
>>     return roots;
>> }
>> ______________________________
>>
>>
>> If I call any of the functions above in a large
>> iteration, will memory start to explode and stress
>> out the garbage collector?
[...]


> Potentially, yes.

Yup. I agree. Its behaving okay for some stuff, but
I do not trust it under prolonged sustained load.


> You want to avoid the intermediate data structures
> obviously, but the question is how? Sadly since
> JavaScript uses CBV evaluation semantics, you won't
> get any help there [1]. Which means it's up to you
> to do some creative thinking in your data structures.

Agreed. For instance, intrusive function design should
work well here. Lets focus on converting the functional
complex multiplication function:
_______________________________________
>> function ct_complex_mul(c0, c1)
>> {
>>     return [c0[0] * c1[0] - c0[1] * c1[1],
>>             c0[0] * c1[1] + c0[1] * c1[0]];
>> }
_______________________________________


into an intrusive form:
_______________________________________
function ct_complex_mul(c0, c1)
{
    var x = c0[0] * c1[0] - c0[1] * c1[1];
    c0[1] = c0[0] * c1[1] + c0[1] * c1[0];
    c0[0] = x;

    return c0;
}
_______________________________________


Now, this will modify (c0), effectively turning it into
an input/output parameter. To call it in a loop could
look like:
_______________________________________
function foo_with_intrusive()
{
    var z = [1, 1];
    var c = [2, 2];

    for (var i = 0; i < 10; ++i)
    {
        z = ct_complex_mul(z, c);
    }
}
_______________________________________



Also, we can do this another way that involves an explicit
output parameter to the function. Something like:
_______________________________________
function ct_complex_mul(c0, c1, out)
{
     out[0] = c0[0] * c1[0] - c0[1] * c1[1];
     out[1] = c0[0] * c1[1] + c0[1] * c1[0];

     return out;
}
_______________________________________


To call it in a loop could look like:
_______________________________________
function foo_with_out()
{
    var out = [0, 0];
    var z = [1, 1];
    var c = [2, 2];

    for (var i = 0; i < 10; ++i)
    {
        out = ct_complex_mul(z, c);
        z[0] = out[0];
        z[1] = out[1];
    }
}
_______________________________________


Notice that both approaches have caveats, but both of them
will not have a chance to create a shi% load of objects!
Do you have some better ideas here?


> Looking at what you have thus far, I don't think
> there is much you can do to improve things at this
> level of discourse, at best I think you might get a
> constant factor speedup at the significant expense
> of readability. (Bit fiddling and Math.foo()
> alternatives...)

FWIW, check out this sqrt estimation algorithm:

http://forums.parallax.com/discussion/147522/dog-leg-hypotenuse-approximation

;^)

> I think what I would do is evaluate how the application
> is developing and at that stage try to discover some
> form of higher level rules that you can exploit. For
> example, for manipulating sums:

> 1 + 2 + 3 + ... + n = (n*(n+1)) / 2

Indeed.

> Another thought is to switch to polar coordinates
> instead of Cartesian coordinates as it would simplify
> multiplication and division at least. With fractal based
> work this might be more intuitive anyway, yes?

Right. However, I think that converting Polar into Cartesian
in order to add/subtract is the simplest route correct?

Thread

Impact of implicit arrays... "Chris M. Thomasson" <nospam@nospam.com> - 2016-06-11 10:52 -0700
  Re: Impact of implicit arrays... Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-06-12 12:16 +0200
    Re: Impact of implicit arrays... "Chris M. Thomasson" <nospam@nospam.com> - 2016-06-13 12:23 -0700
  Re: Impact of implicit arrays... "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2016-06-13 22:00 -0700
    Re: Impact of implicit arrays... "Chris M. Thomasson" <nospam@nospam.com> - 2016-06-14 17:17 -0700
      Re: Impact of implicit arrays... Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-06-15 06:55 +0200
      Re: Impact of implicit arrays... "Chris M. Thomasson" <nospam@nospam.invalid> - 2016-06-14 22:19 -0700
      Re: Impact of implicit arrays... "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2016-06-18 12:47 -0700
        Re: Impact of implicit arrays... "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-06-21 14:43 -0700
          Re: Impact of implicit arrays... "Christoph M. Becker" <cmbecker69@arcor.de> - 2016-06-22 00:10 +0200
            Re: Impact of implicit arrays... "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-06-21 15:28 -0700
              Re: Impact of implicit arrays... "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-06-21 15:31 -0700
                Re: Impact of implicit arrays... "Christoph M. Becker" <cmbecker69@arcor.de> - 2016-06-22 11:55 +0200
                Re: Impact of implicit arrays... "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-06-23 12:23 -0700
                Re: Impact of implicit arrays... "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-06-23 14:14 -0700
                Re: Impact of implicit arrays... "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-06-23 14:16 -0700
                Re: Impact of implicit arrays... "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-06-23 18:14 -0700
                Re: Impact of implicit arrays... "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-06-23 18:46 -0700
          Re: Impact of implicit arrays... "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2016-06-21 17:35 -0700
            Re: Impact of implicit arrays... "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-06-21 21:08 -0700
              Re: Impact of implicit arrays... "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2016-06-21 23:09 -0700
                Re: Impact of implicit arrays... "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-06-23 14:38 -0700
                Re: Impact of implicit arrays... "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2016-06-24 07:16 -0700
                Re: Impact of implicit arrays... "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-06-25 18:03 -0700
                Re: Impact of implicit arrays... "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2016-06-25 18:24 -0700
                Re: Impact of implicit arrays... "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-07-01 13:52 -0700

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