How do I plot many circles using a for-loop on a function?

Hello!

I want to plot 5 circles on one graph with the radius 1 to 5. The conditions are that I need to use a loop of some kind and that it will call the function for the circle 5 times.

I've written a function for plotting a circle:

    function [x,y1,y2]=rita_cirkel(r)
        x=[-1*r:pi/100:r];
        y1=sqrt(r^2-x.^2);
        y2=-1*sqrt(r^2-x.^2);
        plot(x,y1,x,y2);
    end

I tried using a for-loop to plot 5 circles like the following:

    for r=1:1:5
    rita_cirkel(r)
    end

And it didn't work :/ It only game me a graph of a circle with radius=5

I am curious of how do I plot 5 circles in one single graph (like a dart board) while still meeting the conditions of calling a function 5 times and using some kind of loop.

Answer 1

[Walter Roberson]

hold on

Answer 2

[Image Analyst]

You can easily adapt this demo for your (possible) homework problem. It plots circles in random locations:

% M-file to place multiple small circles inside a big circle. 
% Clean up 
close all; 
clc; 
% Initialize some parameters. 
numberOfSmallCircles = 25; % Number of small circles 
smallCircleOutsideValue = 0.2; 
smallCircleInsideValue = 0.8; 
smallCircleRadius = 25;    % small circle radius 
bigImageWidth = 500; 
bigImageHeight =  500; % square area 0f 500*500 
bigCircleRadius = 250;    % big circle radius 

% Initialize an image to hold one single big circle. 
bigCircleImage = zeros(bigImageHeight, bigImageWidth); 
[x, y] = meshgrid(1:bigImageWidth, 1:bigImageHeight); 
bigCircleImage((x - bigImageWidth/2).^2 + (y - bigImageHeight/2).^2 <= bigCircleRadius.^2) = 1; 
% Display it in the upper left plot. 
subplot(3,2,1); 
imshow(bigCircleImage, []); 
title('Big Circle Mask'); 
set(gcf, 'Position', get(0,'Screensize')); % Maximize figure.

% Initialize an image to hold one single small circle. 
smallCircleImage = zeros(2*smallCircleRadius, 2*smallCircleRadius); 
[x, y] = meshgrid(1:smallCircleRadius*2, 1:smallCircleRadius*2); 
singleCircleImage = zeros(2*smallCircleRadius, 2*smallCircleRadius); 
singleCircleImage((x - smallCircleRadius).^2 + (y - smallCircleRadius).^2 <= smallCircleRadius.^2) = smallCircleInsideValue; 
% Display it in the upper right plot. 
subplot(3,2,2); 
imshow(singleCircleImage, []); 
title('Single Small Circle (scaled to fit)'); 

singleWidth = size(singleCircleImage, 2); 
singleHeight = size(singleCircleImage, 1); 
% Get random coordinates in the big image where 
% we will place the upper left corner of the small circle. 
widthThatWillFit = bigImageWidth - 2 * smallCircleRadius; 
heightThatWillFit = bigImageHeight - 2 * smallCircleRadius; 
smallUpperLeftX = widthThatWillFit * rand(numberOfSmallCircles, 1); 
smallUpperLeftY = heightThatWillFit * rand(numberOfSmallCircles, 1); 
% Initialize an output image to hold many small overlapping circles. 
manySmallCircles = zeros(bigImageHeight, bigImageWidth); 
% Place the small circles one by one. 
for k = 1 : numberOfSmallCircles 
        % Find the square in the big image where we're going to add a small circle. 
        x1 = int16(smallUpperLeftX(k)); 
        y1 = int16(smallUpperLeftY(k)); 
        x2 = int16(x1 + singleWidth - 1); 
        y2 = int16(y1 + singleHeight - 1); 
        % Add in one small circle to the existing big image. 
        manySmallCircles(y1:y2, x1:x2) = manySmallCircles(y1:y2, x1:x2) + singleCircleImage; 
end 
% Make outside the circles the outside color. 
manySmallCircles(manySmallCircles == 0) = smallCircleOutsideValue; 
% Display it in the lower left plot. 
subplot(3,2,3); 
imshow(manySmallCircles); 
title('Many Small Overlapping Circles'); 

% Multiply the big circle mask by the many small circles image to clip 
% those small circles that lie outside the big circle. 
maskedByBigCircle = bigCircleImage .* manySmallCircles; 
% Display it in the lower right plot. 
subplot(3,2,4); 
imshow(maskedByBigCircle); 
title('Many Small Circles Masked by Big Circle'); 

% Take the histogram and display it in the bottom row. 
subplot(3,2,5); 
hist(maskedByBigCircle(:));