# ffmatlib3D and matlab

Hello
I’m sorry to bother you, I want to use ffmatlib3D to draw a cross-section of a 3D function, but I don’t know how to select the section. I want to know which parameters are used to select the section. Is it S1, S2, S3 in the figure below?

Thank you very much.

yes that’s right, S1, S2, and S3 all contain three points (which shouldn’t be colinear).

Thank you very much. What do the parameters in S1, S2 and S3 mean respectively? How do you adjust the parameters?

For example,
u=xyz*(1-exp(-(1-x)/epsilon))(1-exp(-(1-y)/epsilon))(1-exp(-(1-z)/epsilon))
I want to draw the figure of z=1 in the numerical solution of u. How should I adjust the parameters in S1, S2 and S3?

It sounds like they are three points that define the plane containing the cross section? So you should define three non-colinear points in your plane of interest. Note that this is a guess since I haven’t actually used this function

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Thank you very much for your answer.I got it, and I’ll try it later.

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The way Chris described is how I understand it, I hope it is working for you!