How to color the space between ellipse?

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

Answer 1

[Torsten]

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

Answer 2

[Vasudev Sridhar]

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)

Answer 3

[Matt J]

fn=@(r) scale( nsidedpoly(1000,'Radius',r) ,[1,2] );

region=subtract(fn(2),fn(1));

plot(region); axis equal; axis([0,4, 0,4]) 

[Matt J]

Or, if you really need the region truncated to the positive quadrant,

fn=@(r) scale( nsidedpoly(1000,'Radius',r) ,[1,2] );

region=subtract(fn(2),fn(1));

region=intersect(region, polyshape([0,0;2,0; 2 4; 0 4]));

plot(region); axis equal;