Finding intersection of polyfit and line

Question

Nicholas 2015-9-16

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/243457-finding-intersection-of-polyfit-and-line

评论： Jan Ulbrich 2020-9-18

I am trying to find the intersection between the polyfit of a line and the line y=1. I have the following code:

polyfit(l,FS,3)
int=roots(polyfit(l)-1)

Essentially, I want the value of length when the Factor of safety is 1:

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

dpb 2015-9-16

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/243457-finding-intersection-of-polyfit-and-line#answer_192668

在 MATLAB Online 中打开

Doesn't do any good to fit the data but not save the coefficients of the resulting fit...

b=polyfit(l,FS,3);     % Get coefficients of polynomial
[~,ix]=min(abs(FS-1)); % Nearest observed point to 1 is
L0=l(ix);              % good guess for starting point
LOne=fsolve(@(b,x) polyval(b,x)-1,L0);  % Solve for x where == 1

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。

Answer 2

Walter Roberson 2015-9-16

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/243457-finding-intersection-of-polyfit-and-line#answer_192672

在 MATLAB Online 中打开

b = polyfit(l,FS,3);     % Get coefficients of polynomial
LOne = roots(b - [0 0 0 1]);
LOneReal = LOne(imag(LOne==0));
LOneInRange = LOneReal >= min(l) && LOneReal <= max(l);

This would be empty if there are no real roots in the range.