How can I draw the fitted curve and find the initial slope of the attached plot?

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Selvarajah Premnath 2021-1-13

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https://ww2.mathworks.cn/matlabcentral/answers/715438-how-can-i-draw-the-fitted-curve-and-find-the-initial-slope-of-the-attached-plot

评论： Star Strider 2021-1-13

采纳的回答： Star Strider

Example.xlsx

Hello, I am just beginner to matlab. Appriciate your help.

I attached the excel file for the x, y data.

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Star Strider 2021-1-13

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/715438-how-can-i-draw-the-fitted-curve-and-find-the-initial-slope-of-the-attached-plot#answer_596638

Try this:

D = readmatrix('Example.xlsx');
x = D(:,1);
y = D(:,2);
p = polyfit(x, y, 3);
yfit = polyval(p, x);
dp = polyder(p);
dyfit = polyval(dp,x(1));
bint = (yfit(1) - dyfit*x(1));
xinitslope = [x(1)-x(75), x(1)+x(75)]; 
yinitslope = dyfit*xinitslope + bint;
figure
plot(x, y)
hold on
plot(x, yfit, 'LineWidth',1.5)
plot(xinitslope, yinitslope, 'LineWidth',3)
hold off
grid
legend('Data', '3\circ Polynomial Fit', 'Initial Slope', 'Location','N')
text(xinitslope(1), yinitslope(1), sprintf('\\leftarrow Initial Slope = %7.2f',dyfit), 'HorizontalAlignment','left', 'VerticalAlignment','middle')