fmincon error in matlab

i need help to solve this ?

partial code is :

%Initial Guess for parameters
P01 = [.2;.4;.04;.1;.02;2];
LB = [0;0;0;0;0;.001]; % Lower Bounds
UB = [.6;.6;.6; .6;.6;inf]; % Upper Bounds
options = optimoptions(@fmincon,'Algorithm','interior-point','Display','off');
% x = fmincon(@(x)x,1,[],[],[],[],0,[],[],options)
[P,sse] =fmincon(@(resid)resid,P01,[],[],[],[],LB,UB,[],options);
% Compare to original
[tpost1,Xpost1] =ode23s(@state,tdata,[y0;x20;x30;zeros(18,1)],[],P(1),P(2),P(3),P(4),P(5),P(6));

error is

Error using fmincon (line 607)
User supplied objective function must return a
scalar value.

Error in soren (line 27)
[P,sse]
=fmincon(@(resid)resid,P01,[],[],[],[],LB,UB,[],options); 
>>

Answer 1

[Brendan Hamm]

Your objective function must return a scalar value but yours is returning a vector as your vector of design variables is a vector; the unchanged input. Consider your objective:

>> Objective = @(resid) resid; % Takes an input and returns it as the output.
>> Objective(1)
ans =
     1
>> Objective([.2;.4;.04;.1;.02;2])
ans =
    0.2000
    0.4000
    0.0400
    0.1000
    0.0200
    2.0000

What is it you are truly trying to minimize? The norm of the vector perhaps?