Data fit problem, 'Data must be numeric, datetime, duration or an array convertible to double.'

Dear all. I am trying to fit my model to data and determine the confidence interval for the fitted parameters. However, when I run my code, I get an error 'Data must be numeric, datetime, duration or an array convertible to double'. I am sure the problem is that "fittedmdl" is an object. I have tried to search related questions online but still I can't seem to get round my problem. Any insight into this will greatly be appreciated. Below is my code.

close all; clear; clc;

x=[100; 101.0932476; 97.12643678; 97.51209399; 96.89011748; 74.54219031; 84.76551121; 58.28584719; 50.17251294; 51.58143659; 48.325];

t=[0; 24; 24; 24; 24; 48; 48; 48; 72; 72; 72;];

fo = fitoptions('Method','NonlinearLeastSquares',...

'Lower',[0,0,0,0],...

'Upper',[Inf,max(t)],...

'StartPoint',[20 0.1 0.1 0.1]);

fittedmdl = fittype('100*A*exp((-C.*(1-exp(-lambda.*t))/lambda)-(D*(exp(-lambda.*t)-1+lambda.*t)/lambda^2))', ...

'independent',{'t'},'coefficients',{ 'A', 'C', 'D', 'lambda'},'options',fo)

[curve2,gof2] = fit(t,x,fittedmdl)

H = plot(fittedmdl,t,x); H(1).MarkerSize = 20; H(1).Color = 'm'; H(2).Color='k';H(2).LineWidth=2;

hold on

xint = linspace(min(t),max(t),1000);

CIF = predint(fittedmdl,xint,0.95,'Functional'); % 95% CI for the fitted curve

plot(t,x,'.m', MarkerSize=20)

hold on

plot(xint,CIF,'-b',linewidth=1)

Answer 1

[Karen Yadira Lliguin León]

you need to use 'fit' (https://es.mathworks.com/help/curvefit/fit.html) first and then you are able to plot the fitobject, something like this:

myfit = fit(x,t,fittedmdl)
H = plot(myfit,t,x);

[Editor]

@Karen Yadira Lliguin León Thank you for your answer. It works well. However, I still get a similar error when executing prediction on this line "CIF = predint(fittedmdl,xint,0.95,'Functional')"

"Incorrect number or types of inputs or outputs for function 'predint'."

[Karen Yadira Lliguin León]

prrdint (https://es.mathworks.com/help/curvefit/cfit.predint.html) need a fitobject, so in your case 'myfit'.

Hope this works for you!

CIF = predint(myfit,xint,0.95,'Functional'); % 95% CI for the fitted curve
plot(t,x,'.m', 'MarkerSize',20)
hold on
plot(xint,CIF,'-b','linewidth',1)

[Editor]

@Karen Yadira Lliguin LeónThank you so much