How to tell whether or not 5 or more lines intersect

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To the left is 4 intersections, and I am trying to control the number of line intersections in my loop. The intersections I am particularly interested are coming from the chords created from intersecting circles. I want to discard iterations that create of 5 or more line intersections. How do I do that?
n = 50; % Number of circles
m = 1000; % Number of points on circle
r_max = 85; % Maximum circle radius
r_min = 30; % Minimum circle radius
x_max = 720; % Uppermost x location of circle center
y_max = 360; % Uppermost y location of circle center
theta = 0:2*pi/m:2*pi; % Evaluated angles for circle
rad = r_max*rand(1,n); % Set radius array size
x_pos = x_max*rand(1,n); % Set x-position array size
y_pos = y_max*rand(1,n); % Set y-position array size
i = 1; % Looping value
j = 1; % Circle data pointer
while i<=n
j = i+1;
while j<=n % Partnering first circle with other circles
[xout,yout] = circcirc(x_pos(i),y_pos(i),rad(i),x_pos(j),y_pos(j),rad(j));
mapshow(xout,yout,'DisplayType','point','Marker','o')
plot(line([xout(1) xout(2)],[yout(1) yout(2)]))
axis([0 x_max 0 y_max]);
hold on
j = j+1;
end
i = i+1;
end

采纳的回答

Jian Wei
Jian Wei 2014-7-21
After you generate the circle centers and their radii, you can run the following code to find the indices of the iterations that create less than 5 intersections.
% find each pair of circles which intersect with each other and store the information in matrix M
M = zeros(n);
for i=1:n-1
for j=i+1:n
if norm([x_pos(i)-x_pos(j),y_pos(i)-y_pos(j)])<rad(i)+rad(j) && norm([x_pos(i)-x_pos(j),y_pos(i)-y_pos(j)])>abs(rad(i)-rad(j))
M(i,j)=1;
M(j,i)=1;
end
end
end
% identify the iteration index which creates less than 5 intersections
index = zeros(n,1);
for i = 1:n
ind = find(M(:,i)~=0);
if ~isempty(ind)
if length(ind)>=5
continue;
else
M1 = M(ind,ind);
if length(ind)+1/2*sum(sum(M1))>=5
continue;
else
index(i)=1;
end
end
end
end
idx = find(index~=0);
The indices of the iterations which create less than 5 intersections are stored in the variable idx. Iterate on idx, and you can discard iterations that create 5 or more than 5 intersections.

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