How to make linear fit?

Question

nancy 2018-6-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/406958-how-to-make-linear-fit

评论： Image Analyst 2018-6-24

test.fig

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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Answer 1

Star Strider 2018-6-22

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https://ww2.mathworks.cn/matlabcentral/answers/406958-how-to-make-linear-fit#answer_325835

在 MATLAB Online 中打开

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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nancy 2018-6-22

Hi,

I want to use polyfit command. But how can I write a code in the script to use polyfit?

Star Strider 2018-6-22

编辑：Star Strider 2018-6-24

在 MATLAB Online 中打开

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