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 — gams:compute_the_median_of_a_parameter_s_values [2009/05/29 12:52] (current)support created 2009/05/29 12:52 support created 2009/05/29 12:52 support created Line 1: Line 1: + ====== How do I compute the median of a parameter'​s values? ====== + The code fragment below  was contributed by Tom Rutherford to the[[http://​www.gams.com/​maillist/​gams_l.htm|GAMS User List]], an example for multidimensional data is available on his web site [[http://​www.mpsge.org/​mdrank.htm|mpsge.org]]. + + <​code>​ + \$title ​ Finding the Median of a Distribution in GAMS + + set     ​i ​      ​Individuals /i1*i1000/; + alias (i,j); + parameter ​      ​income(i) ​      ​Personal income, + rank(i) ​        ​Income rank, + median ​         Median income; + *       Make it random for the purpose of illustration:​ + income(i) = uniform(0,​1);​ + *       This is ugly and slow, but it works: + rank(i) = sum(j\$(income(j) gt income(i)), 1) + 1; + + * In this example there will be no ties, there could be a tie in an arbitrary + * application. ​ Just to be safe,  divide through by the number of + * median individuals:​ + + median = sum(i\$(rank(i) eq round(card(i)/​2)),​ income(i)) + / sum(i\$(rank(i) eq round(card(i)/​2)),​ 1); + + display median; + 