How to color the space between ellipse?

Question

Vivek Bharti 2022-10-26

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https://ww2.mathworks.cn/matlabcentral/answers/1836278-how-to-color-the-space-between-ellipse

评论： Matt J 2022-10-26

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I want to shade the following region :

I know how to plot ellipses using the below code .

But I want to shade the region between two ellipses and I only need x>=0 and y>=0.

In general, if

how do I shade the region when

? Thank you.

ezplot('x^2 + y^2/4 - 1');hold on; ezplot('x^2 + y^2/4 - 4'); hold off

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Answer 1

Torsten 2022-10-26

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编辑：Torsten 2022-10-26

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v = -6:0.001:6; % plotting range from -5 to 5

[x y] = meshgrid(v); % get 2-D mesh for x and y

cond1 = x.^2 + y.^2/4 >= 1; % check conditions for these values

cond2 = x.^2 + y.^2/4 <= 4;

cond3 = x >= 0;

cond4 = y >= 0;

cond1 = double(cond1); % convert to double for plotting

cond2 = double(cond2);

cond3 = double(cond3);

cond4 = double(cond4);

cond1(cond1 == 0) = NaN; % set the 0s to NaN so they are not plotted

cond2(cond2 == 0) = NaN;

cond3(cond3 == 0) = NaN;

cond4(cond4 == 0) = NaN;

cond = cond1.*cond2.*cond3.*cond4; % multiply the conditions to keep only the common points

surf(x,y,cond)

view(0,90) % change to top view

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Answer 2

Vasudev Sridhar 2022-10-26

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Alternative solution in case you are dealing with radial coordinates.

x1 = linspace(0,1,100); % Generate the first set of x coordinates. Change the first two parameters to get different ranges

y1 = 2*sqrt(1-x1.^2);

x2 = linspace(0,2,100); % Generate the second set of x coordinates. Change the first two parameters to get different ranges

y2 = 2*sqrt(4-x2.^2);

x = [x2, fliplr(x1)]; % Get the set of x coordinates for the resultant polygon. The order of the x-coordinates for the second shape shape need to be reversed for this

yeff = [y2, fliplr(y1)]; % Get the set of y coordinates for the resultant polygon. The order of the y-coordinates for the second shape shape need to be reversed for this

fill(x, yeff, 'g'); % Fill the polygon with color green(g)