Findin asymptotes of data curve

Question

Cyril GADAL 2016-6-7

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/288224-findin-asymptotes-of-data-curve

编辑： Cyril GADAL 2016-6-8

Hello everyone !

I'm trying to make a code finding the 2 asymptotes (zero and + infinity) of curve made of data points (so I don't know the theoretical function, and even if I can guess it, this is not the point). Basically, there is a linear asymptote in zero and a constant one in the other side (see pictures).

As you can see, the shape isn't exactly the same, and I would like to find the slope of the first linear part, and the constant at the infinity. Basically, if I can find the point where these two asymptotes are crossing, it's fine. I could use a derivative method but since the slope is very small, the noise in the raw datas is too strong (see next picture).

Any ideas ? I have a lot of these curves so I can't find these 2 asymptotes myself for all.

Thank you !

GADAL Cyril

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Image Analyst 2016-6-7

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/288224-findin-asymptotes-of-data-curve#answer_224715

在 MATLAB Online 中打开

How about if you find out when the data first exceeds the last point, and then fit from then on (basically the flat, right portion of the data) to a line?

firstIndex = find(y > y(end), 1, 'first');
coefficients = polyfit(x(firstIndex:end), y(firstIndex:end), 1);

3 个评论
显示 1更早的评论隐藏 1更早的评论

Image Analyst 2016-6-7

在 MATLAB Online 中打开

One or two data points won't significantly change the slope of the fitted line. However if you want, you can take only indexes within +/- std dev of the line

firstIndex = find(y > y(end), 1, 'first');
theMean = mean(y(firstIndex:end));
theSD = std(y(firstIndex:end));
someFactor = 1.5; % Whatever you want.
indexesToUse = abs(y-theMean) > someFactor * theSD;
coefficients = polyfit(x(indexesToUse), y(indexesToUse), 1);
% Fit the line
fittedY = polyval(coefficients, x);
hold on
plot(x, fittedY, 'r-', 'LineWidth', 3);
grid on;