st: programming in stata - problems with optimize

["A.J van der Vlist" <vlist001@hotmail.com>]

Dear Statalisters,
 
I encouter problems in optimizing function f:
 
I would like to solve for mu:
 
 sum over i {  Nx_i' * (mu - Xbeta_i) } = Sk 
 
Nx = [n x 1] , vector of {1/n}'s  in order to sum over i
mu = parameter 
Xbeta = [n x 1] vector of fitted values
Sk = scalar
 
This is what I tried:
 
scalar Sk1=Sm1_SRA
mata:
X=st_data(.,"Xbeta")
Nx=st_data(.,"Nxi")
void mymodelb(todo, mu2, f, g, H)
{
external Nx, X 
hlp=(mu2 :- X)
f = (Nx' * normal(hlp)) - Sk1 
}
S = optimize_init()
optimize_init_evaluator(S, &mymodelb())
optimize_init_params(S, 0)
mu2 = optimize(S)
problem:
 
1) I get problems when running with Sk1 in f
2) when I substitute for Sk1 =0.501 in f the code will give a result - yet unreasonable high +e11
 
Suggestions are very welcome.
 
Arno 		 	   		  
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