How to plot level curves of f(x,y) = 2x^2 + 5y^2. f(x,y) = c for c = 1,2,3,4,5,6

Asked by Carlos Perez on 10 Apr 2018

Latest activity Edited by Roger Stafford on 10 Apr 2018

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I have never used matlab before and have no idea how to plot level curves. I looked online and most results involve using contour but not exactly sure how to specify the upper limit of z.

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Answer by Birdman on 10 Apr 2018

Edited by Birdman on 10 Apr 2018

Check the output of this code:

f=@(x,y) 2*x.^2 + 5*y.^2;
[X,Y]=meshgrid(-2:0.001:2);
z=f(X,Y);
contour(X,Y,z,[1:6])

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Answer by Roger Stafford on 10 Apr 2018

Edited by Roger Stafford on 10 Apr 2018

Your "level" curves are all ellipses and can most easily be generated by:

t = linspace(0,2*pi);
x = sqrt(c/2)*cos(t);
y = sqrt(c/5)*sin(t);
plot(x,y)
axis equal

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Carlos Perez (view profile)