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Added intergration of Monte Carlo for PHP #431

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Merged
merged 10 commits into from
Oct 7, 2018
Merged

Added intergration of Monte Carlo for PHP #431

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4bc5868
Added intergration of Monte Carlo for PHP
PudottaPommin Oct 3, 2018
b411169
Changed code style
PudottaPommin Oct 4, 2018
559c7fc
Update monte_carlo.php
PudottaPommin Oct 4, 2018
95eafaf
Update monte_carlo.php
PudottaPommin Oct 4, 2018
a7a3738
Update monte_carlo.php
PudottaPommin Oct 5, 2018
afa9d6d
Update monte_carlo.php
PudottaPommin Oct 6, 2018
ed52163
Update monte_carlo.php
PudottaPommin Oct 6, 2018
ec2f420
Update monte_carlo.php
PudottaPommin Oct 7, 2018
e3409c6
Merge branch 'master' into php_monte_carlo
PudottaPommin Oct 7, 2018
4a241aa
Styles fixes and typo
PudottaPommin Oct 7, 2018
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30 changes: 30 additions & 0 deletions contents/monte_carlo_integration/code/php/monte_carlo.php
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Original file line number Diff line number Diff line change
@@ -0,0 +1,30 @@
<?php
declare(strict_types=1);

function in_circle(float $positionX, float $positionY, float $radius = 1): bool
{
return pow($positionX, 2) + pow($positionY, 2) < pow(abs($radius), 2);
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I think you should just do
$positionX * $positionX + $positionY * $positionY + $positionZ * $positionZ
The abs also seems completley unnecessary since x^2 is always positive.

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This still hasn't been resolved btw.

}

function random_zero_to_one(): float
{
return mt_rand(0, 100) / 100;
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Is there a reason for the 100? The recomended way to get a random float is the same as C:
return mt_rand() / mt_getrandmax();

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Yes, there is. We want number in interval <0,1> so I'm getting int in range <0,100> and dividing 100 to get required number

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That results in only 101 posible values 0.000, 0.001, 0.002, ..., 0.999, 1.0, running over 101^2 times would then be meaningless, instead you should take advantage of the full range of floating point precision by dividing by mt_getrandmax()

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I see, it's changed, thanks for explanation :)

}

function monte_carlo(int $samples, float $radius = 1): float
{
$in_circle_count = 0;

for ($i = 0; $i < $samples; $i++) {
if (in_circle(random_zero_to_one(), random_zero_to_one(), $radius))
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x and y position need to be multiplied by $radius for proper range of random values.

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Haven't seen any of the other implementations use radius to multiply X or Y. So what's different in this?

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Other implementations chose for radius to be a constant 1.0, you put radius as a function parameter which default value 1.0
Either you can make radius constant 1.0 or implement it so it correctly calculates pi when the radius parameter is not equal to 1.0
Take a look at the python implementation, they generate random numbers from 0 to radius. The easiest way to do this is just multiply your existing random function by $radius.

$in_circle_count++;
}

return 4 * $in_circle_count / $samples;
}

$piEstimate = monte_carlo(100000000);
$percentError = abs($piEstimate - pi()) / pi() * 100;
echo sprintf('The estimate of PI is: %s', $piEstimate);
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  1. PHP has a printf function
  2. Probably should use %f for these values, php converts em anyway but no harm in being more correct.
  3. Why are we using PHP_EOL rather than \n, it doesn't work for single quote strings but they work fine in double quotes
    printf("The estimate of PI is: %f\n", $piEstimate);

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  1. it has, but there is not much difference and sprintf gives easier way to extract variable
  2. %f would generate X.XXXXX format when %s givex X.XX (depending on number of numbers after dot)
  3. PHP_EOL is constant depending on environment. from SO "PHP_EOL represents the endline character for the current system", so it's much prefered to use it

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Fair enough, I don't understand what you mean by "sprintf gives easier way to extract variable" but your other arguments make sense, I was under the impression PHP would \n to the correct line ending like C/C++.

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it's basically from my experience, where you don't print to console, but you need to work with strings, build them, etc. You can store sprintf to variable and work with it later. printf would print to output.

yes, it would but with PHP_EOL. otherwise if you specify \n it uses that, which might be problem on some platforms.

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@Butt4cak3 Butt4cak3 Oct 4, 2018 •
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You can store sprintf to variable and work with it later.

You do not do that, though, so there's no reason to use it. I have to agree with @Gorzoid here. printf() makes a little more sense.

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I give you this one, I'm gonna change it. But still I'm staying, that sprintf looks better 🤣

echo PHP_EOL;
echo sprintf('The percent error is: %s', $percentError);
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Missing ?> at the end, also should have 1 newline at end of file.

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?> is discouraged and not needed since PHP 5.3 ( I think that version, not sure if 2/3/4 ).
I haven't left newline in any of previous PHP files, so this is with same style and format

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The comment about ?> was a mixup where I thought the code wasn't running because it didn't read a closing tag. It actually was running but was very slow.
The newline requirement is a git requirement rather than a php requirement iirc, Github warns that there is no newline at the end of file. I think it's because it messes with deltas of files.

4 changes: 4 additions & 0 deletions contents/monte_carlo_integration/monte_carlo_integration.md
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Expand Up @@ -71,6 +71,8 @@ each point is tested to see whether it's in the circle or not:
[import:1-4, lang:"ruby"](code/ruby/monte_carlo.rb)
{% sample lang="f90" %}
[import:1-8, lang:"fortran"](code/fortran/monte_carlo.f90)
{% sample lang="php" %}
[import:4-7, lang:"php"](code/php/monte_carlo.php)
{% endmethod %}

If it's in the circle, we increase an internal count by one, and in the end,
Expand Down Expand Up @@ -141,6 +143,8 @@ Feel free to submit your version via pull request, and thanks for reading!
[import, lang:"ruby"](code/ruby/monte_carlo.rb)
{% sample lang="f90" %}
[import, lang:"fortran"](code/fortran/monte_carlo.f90)
{% sample lang="php" %}
[import, lang:"php"](code/php/monte_carlo.php)
{% endmethod %}


Expand Down