Problem using polyfit with NaN data

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Jade Pearson
Jade Pearson 2020-11-18
评论： Jon 2020-11-18
Trying to find Young's Modulus in a specific range. I was to plot the the data for that range, but when I try to get the slope value, it gives me NaN. I worked on the code for days and tried various methods and loopholes, but I can't seem to get it.
data = readtable('TITLE.txt','ReadVariableNames',true);
Load = data.Load(1:end);
Displacement = data.Displacement(1:end);
Strain = data.Strain(1:end);
Strain(Strain < 0.001) = NaN;
plot(Strain)
Strain(Strain > 0.003) = NaN;
plot(Strain)
p = plot(Strain, Load, '.', 'color','r')
title('Youngs Modulus','FontSize', 20);
xlabel('Strain (in/in)', 'FontSize', 15);
ylabel('Load(lbf)', 'FontSize', 15);
polyfit(Strain, Load, 1)
polyval(Strain, Load)

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Jon
Jon 2020-11-18
编辑：Jon 2020-11-18
To avoid having NaN in polyfit I would use
iFit = isfinite(Strain)
c = polyfit(Strain(iFit),Load(iFit))
% ok to have NaN when calculating fitted Load
yfit = polyval(c,Strain)
By the way shouldn't Young's Moduls use Tensile Stress (Load/Area) rather than just raw load?
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Jade Pearson
Jade Pearson 2020-11-18
Understandable. Thank you, I will remember that.
Jon
Jon 2020-11-18
Very nice - I didn't realize you could edit the original question title. Looks very clean now!

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