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% helix.mp
% L. Nobre G.
% 2012
prologues := 1;
beginfig(1);
numeric u, w, i, r, s, lim;
u = 2in;
w = 150;
r = 0.5u;
s = 1/20;
lim = 4;
for i=0 step s until lim:
draw fullcircle scaled 2r shifted (u*(i,sind(i*w)));
endfor;
%draw origin--(u*(90/w,1));
pair d, p;
path slope, decli;
d = (-90/w,3.14159/2);
p = unitvector((-ypart d,xpart d));
slope = ((-u*d)--(u*d)) shifted (-r*p);
decli = reverse slope shifted (2*r*p);
draw (slope--decli--cycle) shifted (u*180/w,0);
endfig;
end.
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