What does this error mean? fminsearch error: "Assignment has more non-singleton rhs dimensions than non-singleton subscripts"

I am trying to Optimize these set of equations to find vector c with i=1,2:

Bold variables are 3D Vectors.

Known Variables: R, o, u1, u2, l1, l2

My code works when I use fsolve but gives me an error for fminsearch

fun.m :

function F = fun(x1,R,o,u1,u2,l1,l2)

c=x1(1:3);
kq1=x1(4);
kq2=x1(5);
q1=x1(6:8);
q2=x1(9:11);
b=x1(12:14);
bnorm=x1(15:17);
kc=x1(18);

F(1:3) = o + kq1*(o-u1) - q1;
F(4:6) = o + kq2*(o-u2) - q2;
F(7) = norm(q1-c) - R;
F(8) = norm(q2-c) - R;
F(9) = (dot((o-q1),(q1-c))*norm(l1-q1)) - (dot((l1-q1),(q1-c))*norm(o-q1));
F(10) = (dot((o-q2),(q2-c))*norm(l2-q2)) - (dot((l2-q2),(q2-c))*norm(o-q2));
F(11:13) = (kc*bnorm)-(c-o);
F(14:16) = (b/norm(b))- bnorm;
F(17:19) = (cross(cross((l1-o),(u1-o)),cross((l2-o),(u2-o)))) - b;

end

script.m :

clear all; clc;
R = 7.8;
o=[0,0,0]; 
u1= [7.4390,7.1380,-0.0607]; 
u2=[6.5360,7.1380,-0.0607]; 
l1=[-83.7542,77.3087,-58.0508]; 
l2=[66.2458,74.8087,-51.0508];

x0 = ones(1,18);
[x fval]= fminsearch(@fun,x0,[],R,o,u1,u2,l1,l2);

OUTPUT:

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Answer 1

[Matt J]

Unlike fsolve, fminsearch is not an equation solver. It minimizes a scalar-valued function. Your code fails because the objective function fun() doesn't return a scalar.

[Alan Weiss]

To elaborate on this answer, you might want to sum the squares of the components of your objective, and pass that to fminsearch.

Alan Weiss

MATLAB mathematical toolbox documentation

[Matt J]

@Goku,

If you do have 18 unknowns, fminsearch is, in any case, unlikely to work well. It is meant for minimizing functions of a small number of variables (typically <= 6).

[Goku]

This helps.

@Alan, I now realize that the output needs to be a scalar value. I made my function to now output the norm(F) instead of F, and that does not give the error. Thank you.

Also, as @Matt J mentions, the objective function doesn't converge well, I would like to see a zero, but it gives value of 5.6196e+05 after 2275 iterations. I will have to make changes to way I solve them. But thank you for pointing that out.