How to minimizing a function depending on last term value ?

I just want to minimizing this function:

Supply(horizon)=exp((x(1)+x(2)*log(It(horizon))+x(3)*log(B1))/(1-B2*x(3)));

f=-sum(Supply);

But It(horizon) changes each horizon .and it depends on the Supply(horizon).

 function f=myfun(x) 
 B1=473610; 
 B2=-1.67; 
 Y=[3.5;5.5]; 
 Ta=[10.522;9.524]; 
 Tmsy=[120;100]; 
 Rc=[6500;8500]; 
 L=[1406;7468]; 
 load('IArea.mat') 
 load('V12.mat') 
 horizon=1;
  while horizon<=200; 
  Stock=IA.*V12./1000; 
  It(horizon)=sum(Stock(1,60:120))+sum(Stock(2,60:120)); 
  Supply(horizon)=exp((x(1)+x(2)*log(It(horizon))+x(3)*log(B1))/(1-B2*x(3))); 
  Pt(horizon)=B1*Supply(horizon)^B2; 

for k=1:2 
for a=60:119 
Eg(k,a)=((Pt(horizon)-95)*V12(k,a+1)+L(k))*exp(-0.03)-((Pt(horizon)-95)*V12(k,a))-L(k); 
end 
for a=1:59 
Eg(k,a)=1000000000; 
end 
Eg(k,120)=((Pt(horizon)-95)*V12(k,120)+L(k))*(exp(-0.03)-1); 
end 
[a,Index]=sort(Eg(:));  
UnitStock=V12.*IA./1000; 

q=0; 
i=1; 
forest1=0; 
forest2=0; 
while Supply(horizon)-q>0; 
q=UnitStock(Index(i))+q; 
[xp,yp]=ind2sub([2 120],Index(i)); 
if xp==1; 
forest1=forest1+IA(Index(i)); 
else 
forest2=forest2+IA(Index(i)); 
end 
IA(Index(i))=0; 
i=i+1; 
end 

[xf,yf]=ind2sub([2 120],Index(i-1)); 
if xf==1; 
forest1=forest1+IA(Index(i-1))-(q-Supply(horizon)).*1000/V12(Index(i-1)); 
else 
forest2=forest2+IA(Index(i-1))-(q-Supply(horizon)).*1000/V12(Index(i-1)); 
end 
IA(Index(i-1))=(q-Supply(horizon))*1000/V12(Index(i-1)); 

IA(:,119) = IA(:,119)+IA(:,120); 
IA(:,[2:120,1]) = IA(:,1:120); 
IA(1,1)=forest1; 
IA(2,1)=forest2; 

horizon=horizon+1 

end 
Supply(horizon)=exp((x(1)+x(2)*log(It(horizon))+x(3)*log(B1))/(1-B2*x(3))); 
f=-sum(Supply);