MATLAB: Circle plot and random point on circle

circlepoints on circlerandom points

Hi,
I drawn a circle on matlab with parametric equations. I give the xcenter,ycenter,r(x1,y1,r1) and the s.S is the number of points which equidistant(have the same distance on circle). I drawn some points on circle and I want to draw 4 random points around. My code is:
t1 = 0:(pi/(5*s1)):2*pi; % s1 is the number of points I want 
x1unit = r1 * cos(t1) + x1; 
y1unit = r1 * sin(t1) + y1;
a1=x1unit(1:10:s1*10); %points around on circle
b1=y1unit(1:10:s1*10);
plot(x1unit, y1unit, 'b', x1, y1, 'ok');%circle 
plot(a1, b1, 'o');
I want random points on circle 3 ,4,or 5 or more on circle.But I couldn't to success it , yes. Could you help me?
Thanks in andvance,

Best Answer

Try this:
% Plot a circle.
angles = linspace(0, 2*pi, 720); % 720 is the total number of points
radius = 20;
xCenter = 50;
yCenter = 40;
x = radius * cos(angles) + xCenter; 
y = radius * sin(angles) + yCenter;
% Plot circle.
plot(x, y, 'b-', 'LineWidth', 2);
% Plot center.
hold on;
plot(xCenter, yCenter, 'k+', 'LineWidth', 2, 'MarkerSize', 16);
grid on;
axis equal;
xlabel('X', 'FontSize', 16);
ylabel('Y', 'FontSize', 16);
% Now get random locations along the circle.
s1 = 5; % Number of random points to get.
randomIndexes = randperm(length(angles), s1)
xRandom = x(randomIndexes);
yRandom = y(randomIndexes);
plot(xRandom, yRandom, 'ro', 'LineWidth', 2, 'MarkerSize', 16);
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