steel.mod:
set PROD;              # products
param rate {PROD} > 0; # tons produced per hour
param avail >= 0;      # hours available in week
param profit {PROD};   # profit per ton
param market {PROD};   # limit on tons sold in week
var Make {p in PROD} >= 0, <= market[p]; #tons produced
maximize Total_Profit: sum {p in PROD} profit[p] * Make[p]; 
                    # Objective: total profits from all products
subject to Time: sum {p in PROD} (1/rate[p]) * Make[p] <= avail;
                    # Constraint: total of hours used by all
                    # products may not exceed available hours

steel.dat:
set PROD := bands coils;
param:    rate  profit  market  :=
  bands   200   25      6000
  coils   140   30      4000
param avail := 40;

Example 1: Input files.