# Can I extract the fully-constructed model from a cfit object, not just the separate pieces of the formula?

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Ellen Maas on 26 Aug 2020
Commented: Ellen Maas on 2 Sep 2020
I have a cfit object that I would like to get the full equation from, with parameter values plugged in. All I have been able to find in my searching so far is "coeffvalues" to get an array of parameter values and "formula" to get the general model form. For example, the cfit object is:
General model Exp1:
val(x) = a*exp(b*x)
Coefficients (with 95% confidence bounds):
a = 3695 (3307, 4083)
b = 9.448e-05 (8.636e-05, 0.0001026)
What I am looking to extract is:
val(x) = 3695*exp(0.00009448*x)
Is this possible?
##### 2 CommentsShow NoneHide None
Steven Lord on 2 Sep 2020
Note that what you're looking to extract is unlikely to give the same results as evaluating the fit object itself. The values of the coefficients that are displayed may not be exactly the same as the values of the coefficients that are stored and used for computations.
Is a exactly 3695 or is it 3695.0000000001?
Ellen Maas on 2 Sep 2020
Yes, I've run into that with Excel. Thank you for pointing it out.

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### Accepted Answer

Ayush Gupta on 2 Sep 2020
There is no direct way to obtain the equation with the substituted parameter values from the 'cfit' object in Curve Fitting Toolbox. However, there is a workaround, a string representation can be generated of the curve from a cfit object, ‘cfit_object’:
equation = formula(cfit_object); %Formula of fitted equation
parameters = coeffnames(cfit_object); %All the parameter names
values = coeffvalues(cfit_object); %All the parameter values
for i = 1:numel(parameters)
param = parameters{i};
l = length(param);
location = regexp(equation, param); %Location of the parameter within the string
while ~isempty(location)
%Substitute parameter value
equation = [equation(1:location-1) num2str(values(idx)) equation(location+l:end)];
location = regexp(equation, param);
end
end
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