# Anonymous Function Error Question

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Brittany Isbister on 10 Mar 2021
Commented: Stephen23 on 11 Mar 2021
Hi All,
I am trying to write an anonymous function that will take the equation and then it will find the parameters for x(1) and x(2). It's telling me that my it can't do it because the size of the left side is 1-by-1 and the size of the right side is 41-by-1. The drug1Dose is a 41x1 structure. Attached is my code. Thank you for your help in advance!
f= @(X,c) c.^X(2)./(X(1)^X(2)+ c.^X(2));
c=drug1Dose;
fun=@(X)f(X,c);
x1=[2,5];
param1=fminsearch(fun,x1)
Stephen23 on 11 Mar 2021
"The drug1Dose is a 41x1 structure. Attached is my code."
So lets try it and see what happens:
drug1Dose = struct('whatever',num2cell(rand(41,1)))
drug1Dose = 41x1 struct array with fields:
whatever
f= @(X,c) c.^X(2)./(X(1)^X(2)+ c.^X(2));
c=drug1Dose;
fun=@(X)f(X,c);
x1=[2,5];
param1=fminsearch(fun,x1)
Operator '.^' is not supported for operands of type 'struct'.

Error in solution (line 2)
f= @(X,c) c.^X(2)./(X(1)^X(2)+ c.^X(2));

Error in solution (line 4)
fun=@(X)f(X,c);

Error in fminsearch (line 200)
fv(:,1) = funfcn(x,varargin{:});

Star Strider on 10 Mar 2021
The problem you want to solve is not at all clear.
It would appear that you are doing curve-fitting (parameter estimation), with independent and dependnet variables. If so, ‘fun’ needs to be:
fun = @(x) norm(c - f(x,t));
assuming that you are estimating the pharmacokinetic parameters of your model sa a function of time.
In any event, ‘fun’ needs to return a scalar, not a vector, for fminsearch (or any other optimisation function) to work correctly.

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