Plot f(x,y) = (x+y+xy+1) / xy = 0

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gunmo gu 2016-6-7

评论： Torsten 2022-12-29

f(x,y) = (x+y+xy+1) / xy = 0

Hi, How can I plot 2D of the function above on MUPAD or Note ? It is simple 2D x, y space but I couldn't figure it out.

Thank you.

Star Strider 2016-6-7

You can do that with the Symbolic Math Toolbox and the fcontour function, setting ‘LevelList’ to a vector of zeros:

syms x y
f(x,y) = (x+y+x*y+1) / (x*y);
figure(1)
fc = fcontour(f);
fc.LevelList = [0 0];

See the documentation on fcontour for details.

Star Strider 2022-12-29

@Matthew — Now, yes. The fimplicit function was introduced in R2016b, so it likely wasn’t available when I posted that answer.

Torsten 2022-12-29

But use

f = @(x,y)(x+y+x*y+1)

to avoid division by 0.

And the zero sets of both functions are equal.

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