$ondollar title USPS (NLP) Example 13.1 of Rardin (1998)

$offsymxref offsymlist offuelxref offuellist offupper
option limrow = 0, limcol = 0;

scalars
a  "land area of territory" /400/,
m  "number of customers in the territory" /200000/,
t  "average time for a carrier at a site" /0.05/,
d  "length of the carrier day" /8.00/,
c  "annual cost per carrier (million)" /0.10/,
u  "annual overhead cost per delivery unit (million)" /0.75/,
k1 "to/from travel time proportionality constant" /0.2/,
k2 "within travel time proportionality constant" /0.1/;

free variables
totcost   "total cost",
x         "number of delivery units";

equations
obj "min total cost";

obj..
totcost =e= u*x + c*( (t*m + k2*sqrt(a*m)) / (d - k1*sqrt(a/x)) );

model usps /all/;

x.l = 1.0;

solve usps using nlp minimizing totcost;