Store Values in Array per Loop iteration issues

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Sam Blake
Sam Blake 2023-11-2
评论： Sam Blake 2023-11-2
Hello everyone. I have a script made to make and analyze the stress strain curves for multiple data sets. I want to store the youngs modulus found in an array "youngs". The modulus is calcualted using polyfit, and then stored in the 'linear_fit' variable. In the code below, you can see at the bottom, i attempt to go and load the first value into 'mod' and then assign it to the 'i'th iterations spot in the 'youngs' array. So since I have 8 data sets, I should see 8 youngs modulus's. However, when I run this code and step through it, only after the first iteration, the 'youngs' array is a 1x386, and by the end of the loop, it is 1x402. I will include a sample data .csv but I cant include all datasets. Anyone that can look through this and spot why it isnt just assigning one value for 'mod' to one value for 'youngs' resulting in a 1 value per for loop iteration data set, id really appreciate that. Once again for clarity, I want to store the value assigned to 'mod' in 'youngs' for each iteration, ultimately making a nx1 array for 'youngs' representing each value derived per for loop iteration. Thank you!
% Loading & Plotting Compression Testing Data
clc;clear;close all
% Data Read
number_files = 8;
youngs = zeros(1,8) ;
for i = 1:number_files
filename = sprintf('DAQ%d.txt', i);
Data = importdata(filename);
%Setting time and pounds variables
time = Data.data(:,3);
PoundsForce = Data.data(:,2);
%Use geometry to convert displacment to strain and pounds to stress
inches = Data.data(:,1);
Area = 2.659044022;
Stress = -1 * (PoundsForce ./ -Area);
Strain = -1 * inches / -.85;
%Cleaning values to only include up to .45 engineering strain
[p,~] = find(Strain > .45 );
Strain(p,:) = [] ;
%Setting strain and stress vectors equal length
Stress = Stress(1:length(Strain),1);
figure;
hold on
% finding linear region by Lower Strain Bound < x > Upper Strain Bound
[i, ~] = find(Strain < 0.01 | Strain > 0.15);
Strain(i, :) = [];
% Normalizing vector length
Stress = Stress(1:length(Strain),1);
% Fitting linear region
[linear_fit,Error] = polyfit(Strain,Stress,1);
[y_fit,delta] = polyval(linear_fit,Strain,Error);
% Evaluating R^2
fit = linear_fit(1).*Strain + linear_fit(2);
SSR = sum((Stress - fit).^2) ; SST = sum((Stress - mean(Stress)).^2);
R_squared = abs(1 - (SSR / SST));
%Plotting strain and stress linear region
OG_Stress = -1 * (PoundsForce ./ -Area);
OG_Strain = -1 * inches / -.85;
Vertical = ones(length(Strain),1);
Vertical = (Vertical .* Strain(end));
Horizontal = ones(length(fit),1);
Horizontal = (Horizontal .* fit(1));
Slope_legend = sprintf('Slope = %d PSI',linear_fit(1));
Rsquared_legend = sprintf('R_squared = %d ',R_squared);
Triangle = plot(Vertical,(Stress+.01),'k--',Strain,Horizontal,'k--',Strain,(fit+.02),'r');
OG_plot = plot(OG_Strain,OG_Stress,'b');
ylim([0,3]);
lgd1 = legend([Triangle(3), OG_plot],{Slope_legend,'Experimental Data'},'Location','southeast');
%title(lgd1,Rsquared_legend);
ylabel('Stress (PSI) ','FontSize',24,'FontWeight','bold') ; xlabel('Strain','FontSize',24,'FontWeight','bold') ;
title('Stress versus Strain Plot','FontSize',24,'FontWeight','bold')
dim = [.4 .007 .2 .2] ; str = 'E' ;
A = annotation("textbox",dim,'string',str,'FitBoxToText','on');
A.EdgeColor = 'none'; hold off
%Plotting 95% confidence error bounds
figure; hold on
plot(Strain,fit+2*delta,'m--',Strain,fit-2*delta,'m--')
%Plotting original stress strain over linear region
Linear_region = plot(Strain,Stress);
%plotting linear fit
Linear_plot = plot(Strain,fit,'r');
ylabel('Stress (PSI) ') ; xlabel('Strain')
title('Stress versus Strain Plot','Linear Region With Line of Best Fit in 95% Confidence')
lgd2 = legend([Linear_plot Linear_region],{Slope_legend,'Experimental Data'},'Location','southeast');
ylim([0,fit(end)]);
title(lgd2,Rsquared_legend)
hold off
% Setting mod to linear_fit(1) - mod should be a 1x1
mod = linear_fit(1) ;
youngs(i) = mod ;
end

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采纳的回答

Torsten
Torsten 2023-11-2
Replace
[i, ~] = find(Strain < 0.01 | Strain > 0.15);
Strain(i, :) = [];
by
[j, ~] = find(Strain < 0.01 | Strain > 0.15);
Strain(j, :) = [];
And rename the variable "mod" ; "mod" is a built-in MATLAB function.

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