Fitting to exp plus a constant

Hello, I am trying to fit some data to an exponential + constant function and have this approach that I came across:

% code is giving good results with template equation : % y = a.*(1-exp(b.*(x-c))) + d;
f = @(a,b,c,d,x) a.*(1-exp(b.*(x-c))) + d;
obj_fun = @(params) norm(f(params(1), params(2), params(3), params(4),x)-y);
sol = fminsearch(obj_fun, [y(end)-y(1),0,0,y(1)]);
a_sol = sol(1);
b_sol = sol(2);
c_sol = sol(3);
d_sol = sol(4);
y_fit = f(a_sol, b_sol,c_sol ,d_sol, x);
figure
plot(x,y,’-+b’,x,y_fit,’-r’); grid on;
legend(‘signal’,’aexp(b(x-c))+d’);
title([‘a=’,num2str(a_sol,’%0.2f’), ‘ b=’,num2str(b_sol),’ c=’,num2str(c_sol),’ d=’,num2str(d_sol)],’FontSize’,14,’Color’,’b’)

Whilst the fit is good, the value of "a" seems wrong (at the expense of "d")

I’ve tried another approach that I came across from Steven Lord (as i don’t really understand the code above)

D=[x y]
% It would be better to parametrize the function as
xmin=min(x);
fitfun = fittype( @(a,b,c,x) a*exp(b*(x-xmin))+c );

[fitted_curve,gof] = fit(D(:,1),D(:,2),fitfun,’StartPoint’,[max(y) -2 min(y)])
plot(fitted_curve,’r-‘)
But I get this error:
Error using fit>iFit (line 362)
Inf computed by model function, fitting cannot continue.
Try using or tightening upper and lower bounds on coefficients.
Error in fit (line 117)
[fitobj, goodness, output, convmsg] = iFit( xdatain, ydatain, fittypeobj, …
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error in PlotAnalysis/FitExp1ContstantButtonPushed (line 1361)
[fitted_curve,gof] = fit(D(:,1),D(:,2),fitfun,’StartPoint’,[max(y) -2 min(y)])
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^Hello, I am trying to fit some data to an exponential + constant function and have this approach that I came across:

Whilst the fit is good, the value of "a" seems wrong (at the expense of "d")

I’ve tried another approach that I came across from Steven Lord (as i don’t really understand the code above)

D=[x y]
% It would be better to parametrize the function as
xmin=min(x);
fitfun = fittype( @(a,b,c,x) a*exp(b*(x-xmin))+c );

[fitted_curve,gof] = fit(D(:,1),D(:,2),fitfun,’StartPoint’,[max(y) -2 min(y)])
plot(fitted_curve,’r-‘)
But I get this error:
Error using fit>iFit (line 362)
Inf computed by model function, fitting cannot continue.
Try using or tightening upper and lower bounds on coefficients.
Error in fit (line 117)
[fitobj, goodness, output, convmsg] = iFit( xdatain, ydatain, fittypeobj, …
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error in PlotAnalysis/FitExp1ContstantButtonPushed (line 1361)
[fitted_curve,gof] = fit(D(:,1),D(:,2),fitfun,’StartPoint’,[max(y) -2 min(y)])
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Hello, I am trying to fit some data to an exponential + constant function and have this approach that I came across:

Whilst the fit is good, the value of "a" seems wrong (at the expense of "d")

I’ve tried another approach that I came across from Steven Lord (as i don’t really understand the code above)

D=[x y]
% It would be better to parametrize the function as
xmin=min(x);
fitfun = fittype( @(a,b,c,x) a*exp(b*(x-xmin))+c );

[fitted_curve,gof] = fit(D(:,1),D(:,2),fitfun,’StartPoint’,[max(y) -2 min(y)])
plot(fitted_curve,’r-‘)
But I get this error:
Error using fit>iFit (line 362)
Inf computed by model function, fitting cannot continue.
Try using or tightening upper and lower bounds on coefficients.
Error in fit (line 117)
[fitobj, goodness, output, convmsg] = iFit( xdatain, ydatain, fittypeobj, …
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error in PlotAnalysis/FitExp1ContstantButtonPushed (line 1361)
[fitted_curve,gof] = fit(D(:,1),D(:,2),fitfun,’StartPoint’,[max(y) -2 min(y)])
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ fit, fminsearch, fittype MATLAB Answers — New Questions

Cart

Cart