Finding the slope after drawing a trend/linear fit
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I have an excel data. I want to find the slope after fitting a linear fit on it. In the attached plot, I manually drawn the fit line in black, I need the matlab code for it. So that the program will do it. I've attached my data too.![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1541602/image.jpeg)
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1541602/image.jpeg)
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Accepted Answer
Star Strider
on 16 Nov 2023
Alternatively —
files = dir('*.xlsx');
T1 = readtable(files.name)
VN = T1.Properties.VariableNames;
T = T1.T;
x = T1.x;
[xmax,idx] = max(x);
idxrng = 1:idx;
DM = [T(idxrng) ones(size(x(idxrng)))]; % Design Matrix
B = DM \ x(idxrng) % Another Option Is 'polyfit'
FitLine = DM * B; % Use 'polyval' With 'polyfit'
xr(1) = 0.004;
yr(1) = [xr 1] * B;
yr(2) = 0.2;
xr(2) = (yr(2)-B(2))/B(1);
figure
plot(T,x)
hold on
plot(T(idxrng), FitLine, '-k', 'LineWidth',3)
plot([1 1]*xr(1), [yr(1) yr(2)], '-r')
plot([xr(1) xr(2)], [1 1]*yr(2), '-r')
hold off
grid
xlabel(VN{1})
ylabel(VN{2})
text(xr(1), yr(2), sprintf('\\uparrow\nSlope = %.2f', B(1)), 'Horiz','left', 'Vert','top')
.
4 Comments
Star Strider
on 17 Nov 2023
If you want regression lines for the outset of each variable, this works —
files = dir('*.xlsx');
T1 = readtable(files.name)
VN = T1.Properties.VariableNames;
T = T1.T;
figure
tiledlayout(2,2)
for k = 1:size(T1,2)-1
nexttile
v = T1{:,k+1};
plot(T, v)
grid
title(VN{k+1})
[vmax,idx] = max(v);
idxrng = 1:idx;
DM = [T(idxrng) ones(size(T(idxrng)))]; % Design Matrix
B = DM \ v(idxrng); % Another Option Is 'polyfit'
FitLine = DM * B; % Use 'polyval' With 'polyfit'
hold on
plot(T(idxrng), FitLine, '-k', 'LineWidth',3)
hold off
xlabel(VN{1})
ylabel(VN{k+1})
text(mean(xlim), 0.9*max(ylim), sprintf('Regression Line Slope = %.3f',B(1)), 'Horiz','center', 'Vert','top')
end
The regression lines do not connect the first and first maximum points in all variables because they are fitting all the data between those points. If you want something else, plese be specific.
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