meshgrid plotting how to speficy x-axis and y-axis values?

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Jeff Eriksen
Jeff Eriksen 2016-10-14
评论： Star Strider 2016-10-14
I create a meshgrid and calculate a function camel. When I plot it, it displays indices, not X and Y values on the plot axes. How can I make it show the X and Y values on the plot axes instead?
[X,Y] = meshgrid(-3:0.1:3); camel = (4-2.1*X.^2+X.^4/3).*X.^2+X.*Y+4*(Y.^2-1).*Y.^2; imagesc(camel)

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回答（1 个）

Star Strider
Star Strider 2016-10-14
I’m not certain what you want to do.
Try this:
[X,Y] = meshgrid(-3:0.1:3);
camel = (4-2.1*X.^2+X.^4/3).*X.^2+X.*Y+4*(Y.^2-1).*Y.^2;
figure(1)
surf(X,Y,camel)
grid on
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Jeff Eriksen
Jeff Eriksen 2016-10-14
Thanks for the additional info. I am more clear now on what each of these do now. I almost always use imagesc to plot a 2D matrix, whether it is correlations, a photograph, or just about anything. Very rarely do I wish to use surf. Now I realize surf works he way I want in this context since I pass it X and Y explicitly. For imagesc and contour, they rely on the indices and have no knowledge of the underlying (x,y) position of the matrix. So now my questions is refined as follows: how can I get imagesc and contour (the latter especially) to display the x,y position on the axes instead of the matric index numbers?
Star Strider
Star Strider 2016-10-14
My pleasure.
The transition of my code to use contour (or here contourf) is straightforward:
[X,Y] = meshgrid(-3:0.1:3);
camel = (4-2.1*X.^2+X.^4/3).*X.^2+X.*Y+4*(Y.^2-1).*Y.^2;
figure(1)
[C,hs] = contourf(X,Y,camel);
grid on
axis equal
view([0, 90])
set(hs, 'LineStyle','none')
To use imagesc requires a couple tweaks:
x = -3:0.1:3;
y = x;
figure(2)
imagesc(x,y,camel)
axis image
Experiment with the resolution of the meshgrid argument and ‘x’ (use the linspace function) to vary the resolution easily.

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