Sierpinski pentagon: Difference between revisions
Added Prolog Solution
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close $fh;</lang>
[https://github.com/SqrtNegInf/Rosettacode-Perl5-Smoke/blob/master/ref/sierpinski_pentagon.svg Sierpinski pentagon] (offsite image)
=={{header|Prolog}}==
{{works with|SWI Prolog}}
This code is based on the Java solution. The output is an SVG file.
<lang prolog>main:-
write_sierpinski_pentagon('sierpinski_pentagon.svg', 600, 5).
write_sierpinski_pentagon(File, Size, Order):-
open(File, write, Stream),
format(Stream, "<svg xmlns='http://www.w3.org/2000/svg' width='~d' height='~d'>\n",
[Size, Size]),
write(Stream, "<rect width='100%' height='100%' fill='white'/>\n"),
Margin = 5,
Radius is Size/2 - 2 * Margin,
pi(Pi),
Side is Radius * sin(Pi/5) * 2,
X is Size/2,
Y is 3 * Margin,
Scale_factor is 1/(2 + cos(2 * Pi/5) * 2),
sierpinski_pentagon(Stream, X, Y, Scale_factor, Side, Order),
write(Stream, "</svg>\n"),
close(Stream).
pi(3.14159265359).
sierpinski_pentagon(Stream, X, Y, _, Side, 1):-
!,
write(Stream, "<path stroke-width='1' stroke='black' fill='blue' d='"),
format(Stream, 'M ~g,~g ', [X, Y]),
pi(Pi),
Angle is 6 * Pi/5,
write_pentagon_points(Stream, Side, Angle, X, Y, 5),
write(Stream, "z'/>\n").
sierpinski_pentagon(Stream, X, Y, Scale_factor, Side, N):-
Side1 is Side * Scale_factor,
N1 is N - 1,
pi(Pi),
Angle is 6 * Pi/5,
sierpinski_pentagons(Stream, X, Y, Scale_factor, Side1, Angle, N1, 5).
write_pentagon_points(_, _, _, _, _, 0):-!.
write_pentagon_points(Stream, Side, Angle, X, Y, N):-
N1 is N - 1,
pi(Pi),
X1 is X + cos(Angle) * Side,
Y1 is Y - sin(Angle) * Side,
Angle1 is Angle + 2 * Pi/5,
format(Stream, 'L ~g,~g ', [X1, Y1]),
write_pentagon_points(Stream, Side, Angle1, X1, Y1, N1).
sierpinski_pentagons(_, _, _, _, _, _, _, 0):-!.
sierpinski_pentagons(Stream, X, Y, Scale_factor, Side, Angle, N, I):-
I1 is I - 1,
pi(Pi),
Distance is Side + Side * cos(2 * Pi/5) * 2,
X1 is X + cos(Angle) * Distance,
Y1 is Y - sin(Angle) * Distance,
Angle1 is Angle + 2 * Pi/5,
sierpinski_pentagon(Stream, X1, Y1, Scale_factor, Side, N),
sierpinski_pentagons(Stream, X1, Y1, Scale_factor, Side, Angle1, N, I1).</lang>
=={{header|Python}}==
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