How to make linear fit?
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Hi; I want to plot a linear fit for the graphic in the attached file. And also I want to calculate slope of this linear fit? How can I do this? File is in the attached file.. Thanks a lot.
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Answers (2)
Star Strider
on 22 Jun 2018
Try this:
I = openfig('test.fig');
Ax = gca;
L1 = findobj(Ax, 'Type','line'); % Find ‘line’ Object
x = L1.XData; % Extract X-Data
y = L1.YData; % Extract Y-Data
XL = [min(x) max(x)]; % Get X-Limits
P = [x(:), ones(size(x(:)))] \ y(:); % Estimate Linear Fit Parameters
LinFit = [XL(:) [1;1]] * P; % Linear Fit
Slope = P(1);
hold on
plot(XL, LinFit, '-r', 'LineWidth',1.5)
hold off
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Star Strider
on 22 Jun 2018
Edited: Star Strider
on 24 Jun 2018
To use polyfit:
I = openfig('test.fig');
L = findobj(gca, 'Type','line'); % Find ‘line’ Object
x = L(2).XData; % Extract X-Data
y = L(2).YData; % Extract Y-Data
x = x(y > -2); % Remove Outliers
y = y(y > -2); % Remove Outliers
XL = [min(x) max(x)]; % Get X-Limits
P = polyfit(x, y, 1); % Estimate Linear Fit Parameters
LinFit = polyval(P, XL); % Linear Fit
Slope = P(1);
figure
plot(x, y)
hold on
plot(XL, LinFit, '-r', 'LineWidth',1.5)
hold off
EDIT — Added plot image.
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