Finding intersection of polyfit and line
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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:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/149140/image.jpeg)
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dpb
2015-9-16
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
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Walter Roberson
2015-9-16
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.
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