How do I constrain a custom model to go through a certain point at a certain slope?

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Quinn Tai 2017-8-1

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https://ww2.mathworks.cn/matlabcentral/answers/351105-how-do-i-constrain-a-custom-model-to-go-through-a-certain-point-at-a-certain-slope

编辑： Veda Upadhye 2017-8-8

I currently have two functions that I am trying to combine into a piecewise continuous function. The left side fits the data very well, so I want to have the right side's fit begin where the left side leaves off. For simplicity sake, let's call this point x. This means I want right_f(x) = left_f(x) and right_f'(x) = left_f'(x).

How do I go about doing this? For what it's worth, the function I'm fitting is of the form f(x)=A/(1+exp(-B*(x-C)))+D on both the left and right sides.

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Answer 1

Veda Upadhye 2017-8-8

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https://ww2.mathworks.cn/matlabcentral/answers/351105-how-do-i-constrain-a-custom-model-to-go-through-a-certain-point-at-a-certain-slope#answer_277299

编辑：Veda Upadhye 2017-8-8

Hi Quinn,

There is a MathWorks blog post which talks about a few ways to constrain a polynomial to go through certain points. It includes some example code and you may customize your code accordingly.

Here is the link to it:

https://blogs.mathworks.com/pick/2015/12/11/polynomial-fit-passing-through-specified-points/

Hope this helps,

Veda