How to draw first order best fit in case of hold on figure?

Question

Safi ullah 2018-1-9

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/376340-how-to-draw-first-order-best-fit-in-case-of-hold-on-figure

评论： Star Strider 2018-1-10

Hi everybody, I have used the following code, and get the fig as shown below.

x = [9.384,39.27];
Y1 = 6.49e-12 * x.^(-4); 
Y2 = 4.36e-10 * x.^(-5); 
Y3 = 1.69e-10 * x.^(-4.3);
loglog(x,Y1,'*') 
hold on
loglog(x,Y2,'*') 
hold on
loglog(x,Y3,'*') 
set(gca,'xtick',[9.384  39.27]);
set(gca,'xticklabel',{'A','B'});

Now I need to draw the best fit between A and B (best fit line draw from points at A towards points at B). I know the best fit in case of simple x and y plot, but due to hold on I do not know how to do this. Any guidance will be appreciated thanks.

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Image Analyst 2018-1-9

在 MATLAB Online 中打开

What does hold on have to do with anything? Are you wanting to know how to use polyfit() to fit a line through the points, like this?

xt = [x(1), x(1), x(1), x(2), x(2), x(2)]
yt = [Y1(1), Y2(1), Y3(1), Y1(2), Y2(2), Y3(2)]
coefficents = polyfit(xt, yt, 1)

Safi ullah 2018-1-9

@ Image Analyst thanks for response. Actually I want to to draw the best fit between the A and B points.

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Answer 1

Star Strider 2018-1-10

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/376340-how-to-draw-first-order-best-fit-in-case-of-hold-on-figure#answer_299407

在 MATLAB Online 中打开

Try this:

x = [9.384,39.27];
Y1 = 6.49e-12 * x.^(-4); 
Y2 = 4.36e-10 * x.^(-5); 
Y3 = 1.69e-10 * x.^(-4.3);
xv = reshape([x; x; x], [], 1);                     % Create X-Vector
YM = reshape([Y1; Y2; Y3], [], 1);                  % Create Y-Vector
DM = [xv(:) ones(size(xv(:)))];                     % Design Matrix
B = DM \ YM;                                        % Estimate Parameters
YFit = DM * B;                                      % Fit Regression For Plot
figure(1)
loglog(x,Y1,'*') 
hold on
loglog(x,Y2,'*') 
loglog(x,Y3,'*')
loglog(xv, YFit, '-r')                              % Plot Regression
hold off
set(gca,'xtick',[9.384  39.27]);
set(gca,'xticklabel',{'A','B'});

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Safi ullah 2018-1-10

@ Image Analyst, actually first I do not understand what you have mentioned in comment. As the answer of Star Strider exactly give me my problem solution and after your second comment I also understand your code. @ Image Analyst and Star Strider thanks both of you.