I want to find inflections point for point data input?

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Vishal Rajpurohit 2018-6-15

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https://ww2.mathworks.cn/matlabcentral/answers/405830-i-want-to-find-inflections-point-for-point-data-input

评论： Vishal Rajpurohit 2018-6-18

采纳的回答： Guillaume

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i have input points

x=[0     1     2     3     4     5     6     7     8     9    10]
y=[5.0000    6.0000    8.0000    9.0000    8.5000    8.0000    7.0000    6.5000    7.0000    8.0000   10.0000]
x1=0:0.001:10;
y1=interp1(x,y,x1,'spline');
plot(x1,y1);

i want to find inflection points on that curve?

explain with full code please.

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采纳的回答

Guillaume 2018-6-15

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https://ww2.mathworks.cn/matlabcentral/answers/405830-i-want-to-find-inflections-point-for-point-data-input#answer_324817

在 MATLAB Online 中打开

The inflections points are when the sign of the difference of your y changes. So, whichever way you obtain your y points (as is or using linear or spline interpolation), the indices of the inflection points are:

inflection_idx = find(diff(sign(diff(y)))) + 1;  %+1 to compensate for the index shift caused by the double diff

Note that linear interpolation won't change the location of the inflection points, it'll still be at y=9 and y=6.5, and even with spline interpolation it's not going to change much.