Common tangents in a symmetric triple well function

Dear Sir/Madam,

I have a problem about finding the common tangents of two local minima of a symmetric triple well function. The function is shown below:

The function is:

The following figures shows the common tangents I want to find out (drawn in the red line). I want to find out the common tangents near the specifc two local minima. Does anyone have any good idea?

PS: I also found a similar question about finding the common tangents and applied my function using that code, but that code only gives me other common tangents and cannot find out the common tangents I wanted here. The similar question link is here for your references:

https://www.mathworks.com/matlabcentral/answers/591076-common-tangent-of-double-well-function

How can I revise this code to find out the common tangents I wanted here?

Thank you very much.

Best regards,

Haiying

[John D'Errico]

Since this is certainly homework, what have you tried? Anyway, the answer you link to already shows an answer. Post a comment on Matt's answer, and explain why you think the solution he offered was inadequate, and what was wrong there?

[Haiying Yang]

I want to find out the two common tangents shown in the red line, not the other two common tangents, Matt's answer can only find out the other two common tangents.

These are the common tangents that I got when using Matt's code, but they actually are not the common tangents I wanted here, how to get the common tangents in the right?

[Haiying Yang]

@Matt J

Matt, How can I get the common tangents in the right shown in my questions?

[John D'Errico]

No. ask on the question MATT Answered. You already know where that is.