diff -r d59bea55db9b -r c445c931472f examples/trick.mod
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/examples/trick.mod	Mon Dec 06 13:09:21 2010 +0100
@@ -0,0 +1,72 @@
+/* TRICK, A Transportation Design Problem */
+
+/* Translated from the Mosel modeling language to GNU MathProg by
+   Andrew Makhorin <mao@gnu.org> */
+
+/* This example model is described in the article "Formulations and
+   Reformulations in Integer Programming" by Michael Trick (it is
+   publicly available at http://mat.gsia.cmu.edu/trick/formul04.pdf).
+
+   This model demonstrates an amazing effect when including in the
+   formulation an additional constraint, which is redundant even for
+   LP relaxation, makes the model easy for solving with the B&B. */
+
+set TRUCKS := 1..10;
+
+set PACKAGES := 1..20;
+
+param capacity{TRUCKS};
+
+param size{PACKAGES};
+
+param cost{TRUCKS};
+
+param can_use{PACKAGES, TRUCKS};
+
+var x{PACKAGES, TRUCKS}, binary;
+
+var y{TRUCKS}, binary;
+
+minimize total: sum{i in TRUCKS} cost[i] * y[i];
+
+f1{i in TRUCKS}:
+      sum{j in PACKAGES} size[j] * x[j,i] <= capacity[i] * y[i];
+
+f2{i in TRUCKS, j in PACKAGES}:
+      x[j,i] <= y[i];
+
+f3{j in PACKAGES}:
+      sum{i in TRUCKS} can_use[j,i] * x[j,i] = 1;
+
+redundant_constraint:
+      sum{i in TRUCKS} capacity[i] * y[i] >= sum{j in PACKAGES} size[j];
+
+data;
+
+param capacity :=
+      [1] 100 [2] 200 [3] 100 [4] 200 [5] 100 [6] 200 [7] 100 [8] 200
+      [9] 100 [10] 200;
+
+param size :=
+      [1] 17 [2] 21 [3] 54 [4] 45 [5] 87 [6] 34 [7] 23 [8] 45 [9] 12
+      [10] 43 [11] 54 [12] 39 [13] 31 [14] 26 [15] 75 [16] 48 [17] 16
+      [18] 32 [19] 45 [20] 55;
+
+param cost :=
+      [1] 1 [2] 1.8 [3] 1 [4] 1.8 [5] 1 [6] 1.8 [7] 1 [8] 1.8 [9] 1
+      [10] 1.8;
+
+param can_use (tr):
+      1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 :=
+   1  1  1  1  1  1  1  0  0  0  0  1  1  1  1  0  0  0  0  0  0
+   2  1  1  1  1  1  1  1  1  0  0  1  1  1  1  1  1  1  0  0  0
+   3  0  1  1  1  1  0  0  0  0  0  0  1  1  1  1  1  1  0  0  0
+   4  0  0  1  1  1  1  1  1  1  1  0  0  1  1  1  1  1  1  0  0
+   5  0  0  1  1  1  1  0  0  0  0  0  0  0  1  1  1  1  1  1  0
+   6  0  0  0  1  1  1  1  0  0  0  0  0  0  1  1  1  0  0  0  0
+   7  0  0  0  0  1  1  1  1  1  0  0  0  0  0  1  1  1  1  0  0
+   8  0  0  0  0  1  1  1  1  1  1  0  0  0  0  0  1  1  1  1  1
+   9  0  0  0  0  0  1  1  1  1  0  0  0  0  0  0  0  1  1  1  1
+  10  0  0  0  0  0  0  0  1  1  1  0  0  0  0  0  0  0  0  1  1;
+
+end;