diff -r d59bea55db9b -r c445c931472f examples/food2.mod
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/examples/food2.mod	Mon Dec 06 13:09:21 2010 +0100
@@ -0,0 +1,150 @@
+/* Food Manufacture 2, section 12.2 in
+ * Williams, "Model Building in Mathematical Programming"
+ *
+ * Sebastian Nowozin <nowozin@gmail.com>
+ */
+
+set oils;
+set month;
+
+/* Buying prices of the raw oils in the next six month. */
+param buyingprices{month,oils};
+
+/* Actual amount bought in each month. */
+var buys{month,oils} >= 0;
+
+/* Stock for each oil. */
+var stock{month,oils} >= 0;
+
+/* Price of the produced product */
+param productprice >= 0;
+param storagecost;
+
+param oilhardness{oils} >= 0;
+param M >= 0;
+
+/* Actual amount of output oil produced in each month */
+var production{m in month} >= 0;
+var useoil{m in month, o in oils} >= 0, <= M;
+var useoilb{m in month, o in oils}, binary;
+
+maximize totalprofit:
+    sum{m in month} productprice*production[m]
+    - sum{m in month, o in oils} buyingprices[m,o]*buys[m,o]
+    - sum{m in month, o in oils} storagecost*stock[m,o];
+
+/* Constraints */
+
+/* 1. Starting stock */
+s.t. startstock{o in oils}:
+    stock[1,o] = 500;
+s.t. endstock{o in oils}:
+    stock[6,o] + buys[6,o] - useoil[6,o] >= 500;
+
+/* 2. Stock constraints */
+s.t. stocklimit{m in month, o in oils}:
+    stock[m,o] <= 1000;
+
+s.t. production1{m in month, o in oils}:
+    useoil[m,o] <= stock[m,o] + buys[m,o];
+s.t. production2{m1 in month, m2 in month, o in oils : m2 = m1+1}:
+    stock[m2,o] = stock[m1,o] + buys[m1,o] - useoil[m1,o];
+
+s.t. production3a{m in month}:
+    sum{o in oils} oilhardness[o]*useoil[m,o] >= 3*production[m];
+s.t. production3b{m in month}:
+    sum{o in oils} oilhardness[o]*useoil[m,o] <= 6*production[m];
+
+s.t. production4{m in month}:
+    production[m] = sum{o in oils} useoil[m,o];
+
+/* 3. Refining constraints */
+s.t. refine1{m in month}:
+    useoil[m,"VEG1"]+useoil[m,"VEG2"] <= 200;
+s.t. refine2{m in month}:
+    useoil[m,"OIL1"]+useoil[m,"OIL2"]+useoil[m,"OIL3"] <= 250;
+
+/* 4. Additional conditions:
+ *    i) The food may never be made up of more than three oils every month
+ */
+s.t. useoilb_calc{m in month, o in oils}:
+    M*useoilb[m,o] >= useoil[m,o];
+s.t. useoilb_limit{m in month}:
+    sum{o in oils} useoilb[m,o] <= 3;
+
+/* ii) If an oil is used in a month, at least 20 tons must be used.
+ */
+s.t. useminimum{m in month, o in oils}:
+    20*useoilb[m,o] <= useoil[m,o];
+
+/* iii) If either of VEG1 or VEG2 is used in a month, OIL2 must also be used
+ */
+s.t. use_oil2a{m in month}:
+    useoilb[m,"VEG1"] <= useoilb[m,"OIL3"];
+s.t. use_oil2b{m in month}:
+    useoilb[m,"VEG2"] <= useoilb[m,"OIL3"];
+
+solve;
+
+for {m in month} {
+    printf "Month %d\n", m;
+    printf "PRODUCE %4.2f tons, hardness %4.2f\n", production[m],
+        (sum{o in oils} oilhardness[o]*useoil[m,o]) / (sum{o in oils} useoil[m,o]);
+
+    printf "\tVEG1\tVEG2\tOIL1\tOIL2\tOIL3\n";
+    printf "STOCK";
+    printf "%d", m;
+    for {o in oils} {
+        printf "\t%4.2f", stock[m,o];
+    }
+    printf "\nBUY";
+    for {o in oils} {
+        printf "\t%4.2f", buys[m,o];
+    }
+    printf "\nUSE";
+    printf "%d", m;
+    for {o in oils} {
+        printf "\t%4.2f", useoil[m,o];
+    }
+    printf "\n";
+    printf "\n";
+}
+printf "Total profit: %4.2f\n",
+    (sum{m in month} productprice*production[m]
+    - sum{m in month, o in oils} buyingprices[m,o]*buys[m,o]
+    - sum{m in month, o in oils} storagecost*stock[m,o]);
+printf "      turnover: %4.2f\n",
+    sum{m in month} productprice*production[m];
+printf "      buying costs: %4.2f\n",
+    sum{m in month, o in oils} buyingprices[m,o]*buys[m,o];
+printf "      storage costs: %4.2f\n",
+    sum{m in month, o in oils} storagecost*stock[m,o];
+
+
+data;
+
+param : oils : oilhardness :=
+    VEG1    8.8
+    VEG2    6.1
+    OIL1    2.0
+    OIL2    4.2
+    OIL3    5.0 ;
+
+set month := 1 2 3 4 5 6;
+
+param buyingprices
+
+:           VEG1    VEG2    OIL1    OIL2    OIL3    :=
+
+1           110     120     130     110     115
+2           130     130     110     90      115
+3           110     140     130     100     95
+4           120     110     120     120     125
+5           100     120     150     110     105
+6           90      100     140     80      135 ;
+
+param productprice := 150;
+param storagecost := 5;
+param M := 1000;
+
+end;