Dear Sir, it worked again. Thank you very much. ... View more

Dear Sir, Thank you for your help last time. The formula you introduced to me to determine the max value of a string is great, and I have applied it to extend my previous problem. This time, it is to change the cost of route into other value, when the route is combined with others (forcing travel on different route with greater distance, rendering higher cost). Everything is fine with the max formula except for the crossmax, which I added in the end to make sure no route with greater cost is obmited for maxlongcost calculation. According to the result, the problem is a bad type, and I think it can be due to the crossmax.  I have checked all the way but still cannot figure out what's wrong with it.  It would be great if you could again help me with this. Thank you very much for your concern.     .    ... View more

Your formula just worked out right, Prof. Thank you very much indeed. Sincerely. ... View more

Thank you for reminding me, the code is posted below ... View more

Here is my code, thank you: Proc optmodel; Set bus={"1","2","3","4","5","6","7","8","9","10","11","12"}; /*bus available*/ Set dep={"C","BS","LT","HS","HX","KTX","TL","NT","HP","TĐ","TL","TN"}; /*departure*/ Number cap{bus}=[45 45 45 45 45 45 45 45 29 29 29 29]; /*bus seats*/ Number dem{dep}=[19 1 50 86 28 116 17 8 31 8 15 4]; /*passengers per route*/ Number cost{bus, dep}=[30 43 32 42 11 38 40 42 35 19 30 38 /*cost of each route when assigned to 45-seat bus*/ 30 43 32 42 11 38 40 42 35 19 30 38 30 43 32 42 11 38 40 42 35 19 30 38 30 43 32 42 11 38 40 42 35 19 30 38 30 43 32 42 11 38 40 42 35 19 30 38 30 43 32 42 11 38 40 42 35 19 30 38 30 43 32 42 11 38 40 42 35 19 30 38 30 43 32 42 11 38 40 42 35 19 30 38 20 29 21 28 7 25 27 28 23 13 20 25 /*cost of each route when assigned to 29-seat bus*/ 20 29 21 28 7 25 27 28 23 13 20 25 20 29 21 28 7 25 27 28 23 13 20 25 20 29 21 28 7 25 27 28 23 13 20 25]; Var x{I in bus, j in dep}>=0; /*passengers on bus i for route j*/ Var y{I in bus, j in dep} binary; /*y=1 if bus i is chosen for route j*/ Min totalcost=sum{i in bus,j in dep}cost[I,j]*Y[i,j]; /*problem is here*/ Constraint demsum{j in dep}:sum{I in bus}X[I,j]>=dem[j]; Constraint caplimit{I in bus}:sum{j in dep}X[I,j]<=cap[I]; constraint nolink{i in bus, j in dep}:X[i,j]-cap[i]*Y[i,j]<=0; Solve; Print X; Print Y; ... View more