diff -r d59bea55db9b -r c445c931472f examples/bpp.mod
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/examples/bpp.mod	Mon Dec 06 13:09:21 2010 +0100
@@ -0,0 +1,83 @@
+/* BPP, Bin Packing Problem */
+
+/* Written in GNU MathProg by Andrew Makhorin <mao@gnu.org> */
+
+/* Given a set of items I = {1,...,m} with weight w[i] > 0, the Bin
+   Packing Problem (BPP) is to pack the items into bins of capacity c
+   in such a way that the number of bins used is minimal. */
+
+param m, integer, > 0;
+/* number of items */
+
+set I := 1..m;
+/* set of items */
+
+param w{i in 1..m}, > 0;
+/* w[i] is weight of item i */
+
+param c, > 0;
+/* bin capacity */
+
+/* We need to estimate an upper bound of the number of bins sufficient
+   to contain all items. The number of items m can be used, however, it
+   is not a good idea. To obtain a more suitable estimation an easy
+   heuristic is used: we put items into a bin while it is possible, and
+   if the bin is full, we use another bin. The number of bins used in
+   this way gives us a more appropriate estimation. */
+
+param z{i in I, j in 1..m} :=
+/* z[i,j] = 1 if item i is in bin j, otherwise z[i,j] = 0 */
+
+   if i = 1 and j = 1 then 1
+   /* put item 1 into bin 1 */
+
+   else if exists{jj in 1..j-1} z[i,jj] then 0
+   /* if item i is already in some bin, do not put it into bin j */
+
+   else if sum{ii in 1..i-1} w[ii] * z[ii,j] + w[i] > c then 0
+   /* if item i does not fit into bin j, do not put it into bin j */
+
+   else 1;
+   /* otherwise put item i into bin j */
+
+check{i in I}: sum{j in 1..m} z[i,j] = 1;
+/* each item must be exactly in one bin */
+
+check{j in 1..m}: sum{i in I} w[i] * z[i,j] <= c;
+/* no bin must be overflowed */
+
+param n := sum{j in 1..m} if exists{i in I} z[i,j] then 1;
+/* determine the number of bins used by the heuristic; obviously it is
+   an upper bound of the optimal solution */
+
+display n;
+
+set J := 1..n;
+/* set of bins */
+
+var x{i in I, j in J}, binary;
+/* x[i,j] = 1 means item i is in bin j */
+
+var used{j in J}, binary;
+/* used[j] = 1 means bin j contains at least one item */
+
+s.t. one{i in I}: sum{j in J} x[i,j] = 1;
+/* each item must be exactly in one bin */
+
+s.t. lim{j in J}: sum{i in I} w[i] * x[i,j] <= c * used[j];
+/* if bin j is used, it must not be overflowed */
+
+minimize obj: sum{j in J} used[j];
+/* objective is to minimize the number of bins used */
+
+data;
+
+/* The optimal solution is 3 bins */
+
+param m := 6;
+
+param w := 1 50, 2 60, 3 30, 4 70, 5 50, 6 40;
+
+param c := 100;
+
+end;