http://support.sas.com/documentation/cdl/en/ormpug/66851/HTML/default/viewer.htm#ormpug_optmodel_gettingstarted03.htm   proc optmodel;    /* specify parameters */   set O={'Detroit','Pittsburgh'};   set D={'Boston','New York'};   number c{O,D}=[30 20                  40 10];   number a{O}=[200 100];   number b{D}=[150 150];   /* model description */   var x{O,D} >= 0;   min total_cost = sum{i in O, j in D}c[i,j]*x[i,j];   constraint supply{i in O}: sum{j in D}x[i,j]=a[i];   constraint demand{j in D}: sum{i in O}x[i,j]=b[j];   /* solve and output */   solve;   print x;     I dont understand assignments c{O, D}. my idea is assign a data step of two columns to this variable.  ... View more