set O;
set D;
param a {i in O};
param r {j in D};
param c {i in O, j in D};
var x {i in O, j in D} >= 0;
minimize cost: sum {i in O, j in D} c[i,j] * x[i,j];
subject to supply {i in O}: sum {j in D} x[i,j] <= a[i];
subject to demand {j in D}: sum {i in O} x[i,j] >= r[j];