How can i determine last infection point of a vector?

Question

Alex Yande 2019-4-28

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/458987-how-can-i-determine-last-infection-point-of-a-vector

评论： dpb 2019-4-28

采纳的回答： dpb

在 MATLAB Online 中打开

I have a vector like this:

A=[1 2 3 173 174 175 176 177 178]

This vector has infection points at 3 and 173. I want to get last inflection point of it. At this example, answer should be 173.

How can i do this?

Thx.

2 个评论
显示无隐藏无

John D'Errico 2019-4-28

编辑：John D'Errico 2019-4-28

An infection point? Is there something contagious involved? Are you asking about a point of inflection instead? If so, then it would appear there is one between points 3 and 4, but one cannot know exacly where.

dpb 2019-4-28

measles seem to be rampant, John... :( mayhaps we should quarantine the thread? :)

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

dpb 2019-4-28

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/458987-how-can-i-determine-last-infection-point-of-a-vector#answer_372652

在 MATLAB Online 中打开

For the type of figure as shown, simple difference will work...

>> d=[0 diff(A)];
>> A(d>4)
ans =
   173
>> 

where the '4' in the test is an arbitrary threshold -- '1' would work for the specific data set; the example would be for data with a larger or possibly slightly variable slope.

More general solution would be to use piecewise regression to find the breakpoints -- how sophisticated solution you need would depend on the real problem characteristics besides the example toy dataset.