The error is straightforward:
Error using fmincon (line 635)
Supplied objective function must return a scalar value.
This is the reason fsolve works, since it is a root-finding algorithm.
In order for this to work with fmincon (and certain other optimisation functions), you would need to do something like this:
[x,fval,exitflag,output] = fmincon(@(x)norm(Obj_Fun(x)),x0,A,b,Aeq,beq,lb,ub)
That will llikely work with fmincon. Whether it produces the desired result is less certain.
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