How to get curve fitting equation

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Abdallah Magour 2024-1-23

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https://ww2.mathworks.cn/matlabcentral/answers/2073436-how-to-get-curve-fitting-equation

评论： Abdallah Magour 2024-1-24

Is there a way I can get the equation shwon in the figure or in the basic fitting window? The 8th degree polynimial.

I want to get this equation through a code line not through the graph tools, I also need it in the exact same form.(Including x)

I will repeiat this for a large number of plots or x and y data directly if possible.

Please ignore the red line at the bottom.

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akshatsood 2024-1-23

编辑：akshatsood 2024-1-23

Hi @Abdallah Magour,

Could you please provide me with the data needed to replicate the issue on my end, allowing me to assist you better?

Abdallah Magour 2024-1-23

Data from a similar graph.xlsx

Hi Akshatsood thank you for your reply, yes I attached a data set in the excel file.

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采纳的回答

Walter Roberson 2024-1-23

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编辑：Walter Roberson 2024-1-23

You would use polyfit

For a degree 8 polynomial, you would probably want to use the centering and scaling, by requesting that S and mu also be returned from polyfit()

To evaluate points at the fitted polynomial, see polyval

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Sam Chak 2024-1-24

在 MATLAB Online 中打开

The data is not the same as what is shown in the image above. However, you can remove the NaN values by utilizing the isnan() function.

T = readtable("Data from a similar graph.xlsx", VariableNamingRule="preserve")

T = 17×2 table

x-axis y-axis _______ __________ -19.88 0.00013017 -14.923 NaN -9.8295 0.00034944 -4.7163 0.00010504 0.42855 0.00010026 5.4723 0.00010318 10.501 0.00010048 15.349 0.00010017 20.066 0.00010005 25.012 0.00010006 29.942 0.00010015 34.999 0.00010153 39.906 0.00010248 44.89 0.00010044 49.954 0.00010016 54.913 0.0001014

x = T{:,1};

y = T{:,2}; % contains NaN

data= [x, y];

%% Omit row contains NaN

data_clean = data(~isnan(data(:, 2)), :)

data_clean = 16×2

-19.8796 0.0001 -9.8295 0.0003 -4.7163 0.0001 0.4286 0.0001 5.4723 0.0001 10.5011 0.0001 15.3487 0.0001 20.0662 0.0001 25.0120 0.0001 29.9422 0.0001

%% Extract from clean data

x_clean = data(:,1);

y_clean = data(:,2);

plot(x_clean, y_clean, '-o'), grid on

Abdallah Magour 2024-1-24

Hi Sam,

This is perfect,exactly what I needed!! Thank you very much.

Works much better than what I have.

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