adding trendline to a plot

Question

Isa Isa 2012-12-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/57253-adding-trendline-to-a-plot

评论： Alex Backer 2020-6-1

Good Day,

Please how do I add trendline(s) to a certain straight line portion(s) of a plot and how to extend the trendline to touch y and or x axis and the y and or x axis value determined?

Another related question is that how do I insert horizontal line on a plot and extend it to touch y axis and the y axis value determined?

Thanks

Best regards,

Isa

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Alex Backer 2020-6-1

See https://www.mathworks.com/matlabcentral/fileexchange/76467-trendline

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Answer 1

Image Analyst 2012-12-23

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https://ww2.mathworks.cn/matlabcentral/answers/57253-adding-trendline-to-a-plot#answer_69265

在 MATLAB Online 中打开

I'd fit the portion of the data you're interested in to a line using polyfit. Then use polyval to get the points on the line over the entire range that you're interested in. See this demo:

clc;    % Clear the command window.
workspace;  % Make sure the workspace panel is showing.
format longg;
format compact;
fontSize = 20;
% Define equation.
x = -2:20;
y = (x-2).^2;
% Plot it
plot(x,y, 'bo-', 'LineWidth', 3);
grid on;
title('y = (x-2).^2', 'FontSize', fontSize);
xlabel('X', 'FontSize', fontSize);
ylabel('Y', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Give a name to the title bar.
set(gcf,'name','Demo by ImageAnalyst','numbertitle','off') 
% Fit the range fro 10 to 20 with a line.
limitedRange = 10:20;
coeffs = polyfit(x(limitedRange), y(limitedRange), 1)
% Define the range where we want the line
xFitting = 0:19; % Or wherever...
yFitted = polyval(coeffs, xFitting);
% Plot the fitted line over the specified range.
hold on; % Don't blow away prior plot
plot(xFitting, yFitted, 'ro-', 'LineWidth', 2);
legend('Original Data', 'Line Fit');

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Image Analyst 2012-12-26

在 MATLAB Online 中打开

I just put your data into my demo and got this. Is this what you want?

clc;    % Clear the command window.
workspace;  % Make sure the workspace panel is showing.
format longg;
format compact;
fontSize = 20;
% Define equation.
x=[ 0 0.2762 0.3488 0.4052 0.5242 0.5806 0.6129 0.6431 0.6673 0.6976 0.7238 0.7520 0.7944 0.8448]; 
y=[ 0 0.0230 0.0370 0.0480 0.0760 0.0900 0.1000 0.1180 0.1380 0.1600 0.1860 0.2130 0.2880 0.4010];
% Plot it
plot(x,y, 'bo-', 'LineWidth', 3);
grid on;
title('y = (x-2).^2', 'FontSize', fontSize);
xlabel('X', 'FontSize', fontSize);
ylabel('Y', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Give a name to the title bar.
set(gcf,'name','Demo by ImageAnalyst','numbertitle','off') 
% Fit the range from index 1 to 14 with a line.
limitedRange = 1:14;
coeffs = polyfit(x(limitedRange), y(limitedRange), 1)
% Define the range where we want the line
xFitting = 9:14; % Or wherever...
yFitted = polyval(coeffs, xFitting);
% Plot the fitted line over the specified range.
hold on; % Don't blow away prior plot
plot(xFitting, yFitted, 'ro-', 'LineWidth', 2);
legend('Original Data', 'Line Fit');

Isa Isa 2013-1-6

Hi, Please assist on this. I try to add trendline to a semilogx plot but didn't succeed. Please check the code below.

% Define equation. x=[ 90868 68151 45434 34076 27261 13631 6816 3408 2273 1948 1705 1137 853 683 569 455 342 274 228 190]; y=[ 3680 3723 3800 3866 3920 4103 4250 4320 4340 4344 4350 4364 4373 4379 4384 4393 4398 4402 4405 4407];

% Plot it semilogx(x,y, 'bo-', 'LineWidth', 3); grid on; % Enlarge figure to full screen. set(gcf, 'units','normalized','outerposition',[0 0 1 1]); % Give a name to the title bar. set(gcf,'name','Demo by ImageAnalyst','numbertitle','off')

% Fit the y data range with a line (limitedRange). limitedRange = 17:20; coeffs = polyfit(x(limitedRange), y(limitedRange), 1); xFitting = linspace(200, 90000, 50); yFitted = polyval(coeffs, xFitting);

% Plot the fitted line over the specified range. hold on; plot(xFitting, yFitted, 'ro-', 'LineWidth', 2); legend('Original Data', 'Line Fit');

Thanks Isa

Ananya Roy 2017-2-20

Hi Isa,

I have similar problem as you had. Please let me know if you could solve that problem and how.

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