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Error using fminunc with array as function output and multiple inputs

Asked by Mikkel Mortensen on 27 Feb 2019
Latest activity Answered by Alan Weiss
on 27 Feb 2019
We are trying to optimize three parameters using fminunc.
Our function contains two for-loops and gives us a probability over time in a vector.
Our parameters for optimization are used in this function as x(1), x(2), x(3)
function P = probabilityFunction(x,T,Tmed)
P = ones(length(T),1)*x(3);
for t=0:T(end)
numPills = sum(Tmed < t);
for i=1:numPills
P(t) = P(t) - x(1)*exp(-x(2)*(t-Tmed(i)));
end
end
end
When we try to run the fminunc, it gives us the error "Supplied objective function must return a scalar value"
We call the fminunc like this:
% pooling the data into one array and sorting
Tmed = [deltaT_mo deltaT_ev]';
Tmed = sort(Tmed);
T = (1:max(Tmed))';
noDrug = 0.5;
E = 0.0025;
v = 0.009;
x0 = [E; v; noDrug];
%%
f = @(x)probabilityFunction(x,T,Tmed);
%%
[x,fval] = fminunc(f,x0);
Should we use another function or is there a way to make the probability as a scalar?
- Thanks

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1 Answer

Answer by Alan Weiss
on 27 Feb 2019

It is not clear what you are trying to do. Your P(x,T,Tmed) is not a scalar, so it is not clear what it means to minimize it.
You might be looking for a least-squares minimization, something like sum(P.^2). If so, you can take your existing objective function and ask lsqnonlin to minimize it. Or you can reformulate your objective function as the sum of squares. For details, see Nonlinear Data-Fitting.
Alan Weiss
MATLAB mathematical toolbox documentation

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