Originally posted by: 1259

Hi

Could any body please help me?

Actually I am programming a production planning model with transportation lead times. I have some constraints as follows:

Stock[t-1]= Qunatity of transport[ t - transport leadtime ]= production[t]+ Stock[t]

for that I do two types of programming:

1:

Stock[0..number ofTimePeriods];

Qunatity of transport[ timeperiods];

forall( t in timeperiods, b in timeperiods: b==t-transport leadtime)  Stock[t-1]= Qunatity of transport[ b]= production[t]+ Stock[t];

2:

forall( t in timeperiods)  Stock[t-1]= Qunatity of transport [ t - transport leadtime]= production[t]+ Stock[t];

Both 1 and 2 does not work. Could any body please guide me how I should deal with this case?

Best regards

Hi

first, the equality constraint is not = but ==

second, to write a==b==c, you should write a==b and then as a second constraint b==c

regards

Originally posted by: 1259

Dear Alex,

Thank you so much for your response..

I really apologize.. Actually a typing error has taken place...

My constrains are as following:

Stock[t-1]+Qunatity of transport[ t - transport leadtime ]= production[t]+ Stock[t]

To deal with the lead time I try two types of progrmming:

Stock[0..number ofTimePeriods];

Qunatity of transport[ timeperiods];

1:

forall( t in timeperiods, b in timeperiods: b==t-transport leadtime) Stock[t-1]+ Qunatity of transport[ b]== production[t]+ Stock[t];

2:

forall( t in timeperiods) Stock[t-1]+ Qunatity of transport [ t - transport leadtime]= =production[t]+ Stock[t];

But nither first nor second works.. Actually I wonder how to I should deal with lead time.

Again thank you so much for your attention

Hi,

here is a small model that works fine:

range timeperiods=1..10;
int transportleadtime=2;
dvar float Stock[0..10];
dvar float Quantityoftransport[-1..10];
dvar float production[timeperiods];
subject to
{
forall( t in timeperiods)
Stock[t-1]+ Quantityoftransport [ t - transportleadtime]==
production[t]+ Stock[t];
}

regards

Originally posted by: 1259

Dear Alex,

Thank you so much for your kind response,

I tried your idea on my model. It works well.

Best regards,