use the result of the fit function as a legend in a plot

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ignacio bobadilla tapia
评论： KSSV 2021-7-29
Hello everyone, I wanted to ask how I can make the legend of the graph be the result of the linear regression that is done with the command 'fit', and that polynomial represent it in the legend, for example y = ax + b, there will be some way to do it automatically or is it done manually?. Thanks.
reg=load('regression.txt')
ft=fit(reg(:,1),reg(:,2),'poly1')
plot(ft,'-r',reg(:,1),reg(:,2),'ob')

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回答（1 个）

KSSV
KSSV 2021-7-29
编辑：KSSV 2021-7-29
Ran in:
load census;
f=fit(cdate,pop,'poly2') ;
h = plot(f,cdate,pop) ;
legendinfo = legend(h) ;
f
f =
Linear model Poly2: f(x) = p1*x^2 + p2*x + p3 Coefficients (with 95% confidence bounds): p1 = 0.006541 (0.006124, 0.006958) p2 = -23.51 (-25.09, -21.93) p3 = 2.113e+04 (1.964e+04, 2.262e+04)
legendinfo.String{2} = formula(f) ;
  2 个评论
ignacio bobadilla tapia
ignacio bobadilla tapia 2021-7-29
@KSSV I want the coefficients to appear in the legend, that is, that p1, p2 and p3 are the numerical values obtained with the fit function, how can it be done?
KSSV
KSSV 2021-7-29
Ran in:
load census;
f=fit(cdate,pop,'poly2') ;
eq = formula(f); %Formula of fitted equation
parameters = coeffnames(f); %All the parameter names
values = coeffvalues(f); %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
h = plot(f,cdate,pop) ;
legendinfo = legend(h) ;
legendinfo.String{2} = eq;
Reference: https://in.mathworks.com/matlabcentral/answers/99155-how-do-i-extract-the-output-equation-from-a-cfit-object-in-curve-fitting-toolbox-2-0-r2009a

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