Plotting a surface in MATLAB

2015 10 3
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更新时间：2015 10 3
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I would like to plot
f(x,y) = x^2*y/(x^2 + y^2)
How do I do this in matlab?

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sally_wu
sally_wu 2015-10-3
编辑：sally_wu 2015-10-3
Maybe like this?
x=2;
y=3;
f(x,y) = x^2*y/(x^2 + y^2);
linspace(x,y)
Anthont Goddard
Anthont Goddard 2015-10-3
I am just getting a load of text output. Not a 3d plot

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Star Strider
Star Strider 2015-10-3

1 个投票

You need to use the meshgrid (or equivalently, ndgrid) function:
x = linspace(-1, 1);
y = linspace(-2, 2);
[X,Y] = meshgrid(x,y);
f = @(x,y) x.^2.*y./(x.^2 + y.^2);
figure(1)
surf(X,Y,f(X,Y))
grid on
I created a function for ‘f’ here, but you could as easily use it simply as:
f = X.^2.*Y./(X.^2 + Y.^2);
and then plot as:
plot(X,Y,f)
I ‘vectorised’ your code to do element-wise operations. See the documentation on Array vs. Matrix Operations for a full discussion.

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Anthont Goddard
Anthont Goddard 2015-10-3
When I run that script I get an error. Subscript indices must either be real positive integers or logicals.
Star Strider
Star Strider 2015-10-3
This code:
x = linspace(-1, 1);
y = linspace(-2, 2);
[X,Y] = meshgrid(x,y);
f = @(x,y) x.^2.*y./(x.^2 + y.^2);
figure(1)
surf(X,Y,f(X,Y))
grid on
ran for me without error, and produced this plot:
Anthont Goddard
Anthont Goddard 2015-10-3
Ah that worked. Thanks :)

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