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

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')

Answer 1

[KSSV]

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) ;

[ignacio bobadilla tapia]

@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]

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