MATLAB: How to display coefficient and offset on graph

coeifficientcurveCurve Fitting Toolboxexponentialfittingrate

I'd like to display some values to plot. What should I do ?

A=xlsread('A.xlsx');
t=A(:,1);
i=A(:,2)/10^(2);
ft = fittype('a*exp(-x/b)+c');
F=fit(t,i,ft)  
b = 1/F.b;
offset = F.c;
plot(t,i);
hold on;
plot(F)
hold  off

It's an example plot, I'd like to make a plot through codes like this figure.

Best Answer

Hi Jaehwi

You can use text function available in MATLAB by specifying the location of text wherever you want.

txt = {'b=0.007','Offset='};

text(220,10.5,txt)

This documentation may help you further

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Can you try this way?

figure,plot(f,'r--');
hold on;
plot(x,y,'^b','MarkerSize',10);

May be because of different class, here 'f' is cfit class

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Similar to how you use the fit command to find the exponential fit, you can use it to find the linear fit by using 'poly1' as the fitType argument. Please see the fitType section of the fit documentation for information.

To display the equations on on the plot, you can implement this workaround from a similar MATLAB Answers question.

Assuming you would like to display the equation in the plots legend, please try the below code:

x = SZA15(:,9);
y = SZA15(:,5);  
fits{1} = fit(x,y,'exp1'); %Exponential Fit Model
fits{2} = fit(x,y,'poly1'); %Linear Fit Model
hold on
plot(x,y,'o'); %Plot raw data as circles
plot(fits{1},'r');
plot(fits{2},'b');
str = {'Data'};
%Extact the equations
for i = 1:numel(fits)
    % Generate the equation for each fit
    eq = formula(fits{i}); %Formula of fitted equation
    parameters = coeffnames(fits{i}); %All the parameter names
    values = coeffvalues(fits{i}); %All the parameter values
        for idx = 1:numel(parameters)
              param = parameters{idx};
              l = length(param);
              loc = regexp(eq, param); %Location of the parameter within the string
              while ~isempty(loc)   
                  %Substitute parameter value
                  eq = [eq(1:loc-1) num2str(values(idx)) eq(loc+l:end)];
                  loc = regexp(eq, param);
              end
        end
        str{i+1} = eq; %append fit equation
end
legend(str); %display equations in legend

Best Answer

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