diff -r d59bea55db9b -r c445c931472f examples/sorting.mod
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/examples/sorting.mod	Mon Dec 06 13:09:21 2010 +0100
@@ -0,0 +1,67 @@
+/* sorting.mod - how to sort arrays in MathProg */
+
+/* Written in GNU MathProg by Andrew Makhorin <mao@gnu.org> */
+
+#  Sometimes it is necessary to print parameters or variables in the
+#  order of ascending or descending their values. Suppose, for example,
+#  that we have the following subscripted parameter:
+
+set I := 1..12;
+
+param a{i in I} := Uniform(2, 7);
+
+#  If we print all its members:
+
+printf{i in I} "a[%d] = %g\n", i, a[i];
+
+#  the output may look like follows:
+#
+#  a[1]  = 2.64156
+#  a[2]  = 2.04798
+#  a[3]  = 2.14843
+#  a[4]  = 4.76896
+#  a[5]  = 6.09132
+#  a[6]  = 3.27780
+#  a[7]  = 4.06113
+#  a[8]  = 4.05898
+#  a[9]  = 6.63120
+#  a[10] = 6.50318
+#  a[11] = 3.46065
+#  a[12] = 4.69845
+#
+#  However, we would like the parameter members to appear in the order
+#  of ascending their values.
+#
+#  Introduce the following auxiliary parameter:
+
+param pos{i in I} :=
+      1 + card({j in I: a[j] < a[i] or a[j] = a[i] and j < i});
+
+#  where pos[i] = k means that in the sorted list member a[i] would
+#  have k-th position, 1 <= k <= |I|. Then introduce another auxiliary
+#  parameter:
+
+param ind{k in 1..card(I)} := sum{i in I: pos[i] = k} i;
+
+#  where ind[k] = i iff pos[k] = i.
+#
+#  Now, the following statement:
+
+printf{k in 1..card(I)} "a[%d] = %g\n", ind[k], a[ind[k]];
+
+#  prints the parameter members in the desired order:
+#
+#  a[2]  = 2.04798
+#  a[3]  = 2.14843
+#  a[1]  = 2.64156
+#  a[6]  = 3.27780
+#  a[11] = 3.46065
+#  a[8]  = 4.05898
+#  a[7]  = 4.06113
+#  a[12] = 4.69845
+#  a[4]  = 4.76896
+#  a[5]  = 6.09132
+#  a[10] = 6.50318
+#  a[9]  = 6.63120
+
+end;