Parameter fitting using nlinfit (high order ODEs)

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Learner
Learner 2014-9-5
评论： Star Strider 2014-9-6
I am trying to fit data on multi-dimensional ODEs:
function output = myfunc(pars,tspan)
% we just rename the variable here for use in the ODE
k = pars;
function dCadt = ode(t,Ca)
% this is the ODE we are fitting to
dCadt(1) = -k(1)*Ca(1);
dCadt(2) = k(2)*Ca(1)*Ca(2);
end
% Initial concs. of Ca.
Cao = [2 3]';
[t,Ca] = ode15s(@ode,tspan,Cao);
output = Ca;
end % myfunc
Calling function:
tspan = [0 0.1 0.2 0.4 0.8 1]';
Cadata = [2.0081 1.5512 1.1903 0.7160 0.2562 0.1495;
2.0081 1.5512 1.1903 0.7160 0.2562 0.1495]';
parguess = [1.3 2]; % nonlinear fits need initial guesses
[pars, resid, J] = nlinfit(tspan,Cadata,@myfunc,parguess)
However it always give this error:
Error using nlinfit (line 185)
Requires a vector second input argument.
When I run same program with lsqcurvefit, it runs smoothly!
Please anyone help me to sort this error!

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回答（1 个）

Star Strider
Star Strider 2014-9-5
That has to do with differences between lsqcurvefit (that will fit matrix dependent variables) and nlinfit that will only fit vector dependent variables.
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Learner
Learner 2014-9-6
Is it possible to use 'nlparci' with lsqcurvefit?
Or do you know any other command similar to nlparci which can be used with lsqcurvefit?
Thanks in advance.
Star Strider
Star Strider 2014-9-6
I don’t remember if nlparci will work when you’re fitting two dependent variables, since it’s been a while since I tried that. I believe it will, but I know nlpredci will not.

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