Syntax Error

[Senam Sedzro]

Hi All,

I encounter the following errors: ''t is undefined" and "j is undefined". I am solving a supply-demand scheduling problem. I indexed the set of demand I and the set of suppliers J. T is the time horizon.

My objective  is to jointly minimize the supplier and consumer costs: 

Min CC+SC ;  

s.t. CC=sum{t in 1..T} sum{i in I} z[i,t]*demand[i,t]*dc[t];

​s.t. SC=sum{t in 1..T} sum{j in J} w[j,t]*supply[j,t]*sc[j,t];​

​. . .

Prior to the objective and the variable definition, I defined the sets and parameters. I don't really know why I am getting these errors for the 2nd constraint.

Thank you for helping me out.​

--

​Senam

[victor.z...@gmail.com]

Hi Senam,

Constraint names are missing from your declarations. here's a corrected declaration (provided that CC, T, etc. are defined appropriately):

  s.t. cc_con: CC=sum{t in 1..T} sum{i in I} z[i,t]*demand[i,t]*dc[t];

where cc_con is the constraint name.

HTH,

Victor

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[Senam]

Hi Victor,

Thanks for your answer. In fact, below is the complete form of what I wrote (objective and the 2 constraints):

minimize Total_Cost: alpha*CC+(1-alpha)*GC;

 subject to const01: CC = sum {t in 1..T} (B*(1+Klow*Xlow[t]+Khigh*Xhigh[t])+Ehigh[t]*(1+Khigh)-Elow[t]*(1+Klow))*Cbase;

 subject to const02: GC = sum {t in 1..T} sum {j in J} w[j,t]*Pg[j,t]*C[j]+su[j,t]*SUC[j]; 

Thanks,

Senam

[victor.z...@gmail.com]

You get an error in the second constraint because the sum operator has the same precedence as binary + and addition is left associative, so const02 is equivalent to

  subject to const02: GC = (sum {t in 1..T} sum {j in J} w[j,t]*Pg[j,t]*C[j])+su[j,t]*SUC[j]; 

and therefore j and t are not in scope for the term su[j,t]*SUC[j]. This can be fixed by adding parentheses:

  subject to const02: GC = sum {t in 1..T} sum {j in J} (w[j,t]*Pg[j,t]*C[j]+su[j,t]*SUC[j]); 

HTH,

Victor

[Senam]

Oh.... I see!

Thank you Victor.

It is hard to find these small details.

Thank you so much Victor!

Senam