Constraint _scon[1] is not convex quadratic since it is an equality constraint.

[Nadia Ch]

Hi everybody, 

I am executing my model with CPLEX and AMPL show me the following 

CPLEX 12.5.1.0: Constraint _scon[1] is not convex quadratic since it is an equality constraint.

Althought all my constraints are linear. 

Here are all my constraints of the model :

#Constraints

subject to const1{i in V}: sum{j in Pf[i]} f[i,j]-sum{j in Pb[i]} f[j,i]=b1[i]*sum{(entr,j) in E} f[entr,j]; 

subject to const2{(i,j) in E}: f[i,j]<=q[i,j]; 

subject to const3{(i,j) in E}: qmin[i,j] <= q[i,j] <= qmax[i,j]; 

subject to const4{(i,j) in E}: 1 <= 1/x[i,j]*(qmax[i,j]-q[i,j]) <= qmax[i,j]-qmin[i,j];

subject to const5{(i,j) in E}: 1 <=1/y[i,j]* (q[i,j]-qmin[i,j]) <= qmax[i,j]-qmin[i,j];

subject to const6{u in Ag, (i,j) in Eu[u]}: deltaF[i,j,u]= - c[i,j] +(c[i,j]-M)*(1-x[i,j]);

subject to const7{u in Ag, (i,j) in E diff Eu[u]}: deltaF[i,j,u]= -M ;#(i,j) in E but not in Eu[u]

subject to const8{u in Ag, (i,j) in Eu[u]}: deltaB[i,j,u]= c[i,j] -(c[i,j]+M)*(1-y[i,j]) ;

subject to const9{u in Ag, (i,j) in E diff Eu[u]}:deltaB[i,j,u]= -M*(1-y[i,j]);

subject to const10{(i,j) in E,u in Ag}: t[j,u]-t[i,u]>=deltaF[i,j,u];

subject to const11{(i,j) in E,u in Ag}: t[i,u]-t[j,u]>=deltaB[i,j,u];

subject to const12{i in V, u in Ag}: sum{j in Pf[i]} phi[i,j,u]-sum{j in Pb[i]} phi[j,i,u]=b2[i]; 

subject to const13{u in Ag}: t[exit,u] <= sum{(i,j) in E} psi[i,j,u];

subject to const14{u in Ag}: t[exit,u] <= wu[u] * pi; 

subject to const15{(i,j) in E, u in Ag}: psi[i,j,u] >= -M;

subject to const16{(i,j) in E, u in Ag}: psi[i,j,u] <= phi[i,j,u]*c[i,j];

subject to const17{(i,j) in E, u in Ag}: psi[i,j,u] <= deltaF[i,j,u];

subject to const18{(i,j) in E, u in Ag}: psi[i,j,u] >= M*(phi[i,j,u]-1)+deltaF[i,j,u];

What is the probem? Please could some one help me?

Thanks a lot 

[Robert Fourer]

To see the constraint that CPLEX is rejecting, use the command "expand _scon[1];".

 

Perhaps you are multiplying a variable by another variable in an equality constraint, which is something that CPLEX cannot handle.  It is hard for me to tell, however, since I do not know which are the variables and which are the parameters in your model.

 

Bob Fourer

am...@googlegroups.com

 

 

From: am...@googlegroups.com [mailto:am...@googlegroups.com]

On Behalf Of Nadia Ch
Sent: Wednesday, November 20, 2013 4:29 AM
To: am...@googlegroups.com
Cc: Nadia Ch
Subject: [AMPL 7677] Constraint _scon[1] is not convex quadratic since it is an equality constraint.

[Nadia Ch]

Thanks a lot for your advices. I used the command "expand _scon[1];" and effectively I found the constraint that it was responsible for this error and it was a multiplication of 2 variables.