Hello everyone,
so I've been working on a code which first asks a user what part of the data is linear by asking for the start point x value (or strain in this case) of the linear region of a graph(aka C1_Strain_Start), and the x value of the end of the linear section(aka C1_Strain_End).
After it has done that, I want it to make it fit a first order polynomial to it, in order to extract the slope (which is stiffness in my case). Here is the code I have:
m=1;
while Cycle1UpStrain(m,1)<C1_Strain_Start
m=m+1;
end
n=1;
while Cycle1UpStrain(n,1)<C1_Strain_End
n=n+1;
end
C1_Strain_Stiffness_pts(m:n,1)=Cycle1UpStrain(m:n,1);
C1_Stress_Stiffness_pts(m:n,1)=Cycle1UpStrain(m:n,1);
Stiffness_Eqn1 = [5 5];
Stiffness_Eqn1 = polyfit(C1_Strain_Stiffness_pts,C1_Stress_Stiffness_pts,1);
Stiffness1=Stiffness_Eqn1(1,1)
In here C1_Strain_Start and C1_Strain_End are the start and end x values I spoke of earlier, Stiffness_Eqn1 is the polyfit coefficients, and Stiffness1 would be the slope.
Cycle1UpStrain and Cycle1UpStress are all the data points including non-linear region. C1_Strain_Stiffness_pts and C1_Stress_Stiffness_pts extracts only the linear region as designated by the user's earlier input.
So am I using polyfit wrong? it keeps giving me a polyfit of [1, 1.6x10^-17] (the second value changes a bit, but is usually x10^-17 or x10^-18) for ANY values I give it when I runt he program. Which shows something is wrong.
Thanks for your time!
Neil
