Shading area between 2 curves (x function in terms of y)

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rezheen
rezheen 2025-6-25
编辑： rezheen 2025-7-1
Ran in:
Hello, I'm trying to shade an area between two functions (x depending on y), I shade the correct area but I get a reflection of that shaded region possibly about the line y=x. I don't want this reflection in my graph, I only want the shaded region. Here's my code:
syms x y
x1=y^2; x2=y^3; y1=0; y2=1; % y1 & y2 are the boundaries
fp1 = fplot(x1, [y1 y2]); hold on; grid on;
fp2 = fplot(x2, [y1 y2]);
ylim('padded')
x1 = fp1.XData;
y1 = fp1.YData;
x2 = fp2.XData;
y2 = fp2.YData;
patch([y1 fliplr(y2)], [x1 fliplr(x2)], 'g'); hold off;

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Paul
Paul 2025-6-25
移动：Paul 2025-6-25
Ran in:
Here are the plots of the functions. The independent variable is y, which spans the x-axis on the fplot
syms x y
x1=y^2; x2=y^3; y1=0; y2=1; % y1 & y2 are the boundaries
fp1 = fplot(x1, [y1 y2]); hold on; grid on;
fp2 = fplot(x2, [y1 y2]);
ylim('padded')
xlabel('y')
ylabel('x')
To shade the region in between we have to note that the xdata is actually the YData of the plot and the ydata is actually the XData of the plot, because we are plotting x = f(y);
figure
fp1 = fplot(x1, [y1 y2]); hold on; grid on;
fp2 = fplot(x2, [y1 y2]);
ylim('padded')
xlabel('y')
ylabel('x')
%x1 = fp1.XData;
%y1 = fp1.YData;
%x2 = fp2.XData;
%y2 = fp2.YData;
y1 = fp1.XData;
x1 = fp1.YData;
y2 = fp2.XData;
x2 = fp2.YData;
patch([y1 fliplr(y2)], [x1 fliplr(x2)], 'g'); hold off;
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Paul
Paul 2025-6-30
I don't understand what you want to do for the three-curve case. How should y3 = 2 influence the result?
rezheen
rezheen 2025-7-1
编辑：rezheen 2025-7-1
@Paul: y1 to y3 are the limits of integration and the functions are x depending on y. The intersection points of x=3-y, with x=2*sqrt(y) is at y=1 and 3-y and (y-1)^2 intersect at y=2, so I plotted them based on those intersection points, sort of patching all three curves together. @the cyclist's 'visible off' method allowed me to just plot the patched areas where they're filled, but with the code you provided, I got an incorrect plotting of the curve x=2*sqrt(y) or an additional curve underneath it that I wasn't able to get rid of. Both of your codes are great and I used them for different purposes.

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更多回答（2 个）

the cyclist
the cyclist 2025-6-25
编辑：the cyclist 2025-6-25
Ran in:
I think you got yourself -- and me -- confused by swapping the definitions of what are conventionally called the X- and Y-axis.
Is this what you want? Or did you want the lower one?
syms x y
% Note that I changed the function definitions in this line
x1=y^(1/2); x2=y^(1/3); y1=0; y2=1; % y1 & y2 are the boundaries
fp1 = fplot(x1, [y1 y2]); hold on; grid on;
fp2 = fplot(x2, [y1 y2]);
ylim('padded')
x1 = fp1.YData; % In these lines, you need to be careful that MATLAB calls
y1 = fp1.XData; % the horizontal axis "X", but that is what you call "Y".
x2 = fp2.YData;
y2 = fp2.XData;
patch([y1 fliplr(y2)], [x1 fliplr(x2)], 'g'); hold off;
the cyclist
the cyclist 2025-6-29
编辑：the cyclist 2025-6-30
Ran in:
Another (I think simpler) method is to change the "view" of the axes.
This way the XData and YData properties of line up with what you expected. If you label your axes -- which you should -- then those do need to be swapped (because of the view change).
syms x y
x1=y^2; x2=y^3; y1=0; y2=1; % y1 & y2 are the boundaries
fp1 = fplot(x1, [y1 y2]); hold on; grid on;
fp2 = fplot(x2, [y1 y2]);
xlim('padded')
x1 = fp1.XData;
y1 = fp1.YData;
x2 = fp2.XData;
y2 = fp2.YData;
patch([x1 fliplr(x2)],[y1 fliplr(y2)],'g');
xlabel("y")
ylabel("x")
view([90 -90])

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