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Jun 29, 2018
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Add D implementation of monte carlo #162

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bed144f
Add d implementation of monte carlo
SirSireesh Jun 29, 2018
6fb67d4
cleanup d version of monte carlo
SirSireesh Jun 29, 2018
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29 changes: 29 additions & 0 deletions chapters/monte_carlo/code/d/monte_carlo.d
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Original file line number Diff line number Diff line change
@@ -0,0 +1,29 @@
///Returns true if a point (x, y) is in the circle with radius r
bool inCircle(double x, double y, double r = 1.0)
{
return x ^^ 2 + y ^^ 2 < r ^^ 2;
}

///Calculate pi using monte carlo
real monteCarloPI(ulong n)
{
import std.algorithm : count;
import std.random : Random, uniform01, unpredictableSeed;
import std.range : generate, take;
import std.typecons : tuple;

auto rnd = Random(unpredictableSeed);
return generate(() => tuple!("x", "y")(rnd.uniform01, rnd.uniform01))
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I think we should make this part a little more explicit, something like:

    auto radius = 1.0;
    auto piCount = generate(() => tuple!("x", "y")(rnd.uniform01, rnd.uniform01))
        .take(n)
        .count!(a => inCircle(a.x, a.y, radius));
    return 4.0 * piCount / (n * radius * radius);

I definitely think radius should be a variable just or clarity's sake and with that change, jamming the return value into one expression seems a bit over the top.

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I can do the return bit, but its worth noting that the Julia code is being refactored to remove the radius variable entirely. I think that would be better.

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Removing radius also works but I'd still introduce the separate variable for piCount.

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done

.take(n)
.count!(a => inCircle(a.x, a.y)) / cast(real) n * 4.0;
}

void main()
{
import std.math : abs, PI;
import std.stdio : writeln;

auto p = monteCarloPI(100_000);
writeln("Estimated pi: ", p);
writeln("Percent error: ", abs(p - PI) * 100 / PI);
}
5 changes: 5 additions & 0 deletions chapters/monte_carlo/monte_carlo.md
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Expand Up @@ -45,6 +45,8 @@ each point is tested to see whether it's in the circle or not:
[import:7-7, lang:"haskell"](code/haskell/monteCarlo.hs)
{% sample lang="rs" %}
[import:7-9, lang:"rust"](code/rust/monte_carlo.rs)
{% sample lang="d" %}
[import:2-5, lang:"d"](code/rust/monte_carlo.d)
{% endmethod %}

If it's in the circle, we increase an internal count by one, and in the end,
Expand Down Expand Up @@ -88,6 +90,9 @@ Feel free to submit your version via pull request, and thanks for reading!
{%sample lang="rs" %}
### Rust
[import, lang:"rust"](code/rust/monte_carlo.rs)
### D
{%sample lang="d" %}
[import, lang:"d"](code/d/monte_carlo.d)
{% endmethod %}


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