[Scip] Adding variables and Constraints to MIP

[sheetal murkute]

Hi Gerald,
This solved my problem.
Thank you!


- Sheetal

On Wed, Mar 7, 2012 at 5:08 PM, Gerald Gamrath <gamrath at zib.de> wrote:

>  Dear Sheetal,
>
> if you want to create a variable without upper bound, you should set the
> upper bound to infinity, by giving SCIPinfinity(scip) instead of NULL to
> the SCIPcreateVar() method. NULL is just a null pointer and is interpreted
> as an upper bound of 0, such that all variables that you create are fixed
> to 0.
>
> I hope that helps and solves your problem. If not, please tell us and we
> will have a closer look.
>
> Best,
> Gerald
>
> Am 07.03.2012 22:51, schrieb sheetal murkute:
>
> Hi,
> I have written a code for solving MIP. I did not get any compilation
> error, however,
> the solution comes out to be infeasible, which is incorrect. There might
> be some error in creating constraints and variables for SCIP.
>
>  I want to create continuous variables >= 0. For this I have set lower
> bound as 0, upper bound NULL and type SCIP_VARTYPE_CONTINUOUS.
> Is this correct? All the codes in examples folder in SCIP are having
> bounded variables, hence I am not sure about this.
>
>          std::vector<SCIP_VAR*> _vars;
>     ostringstream namebuf;
>
>  // create xijk variables and add to problem, store to the std vector for
> later use
>  for(i=1;i<=A*K;i++)
>  {
>  SCIP_VAR* var;
>  namebuf.str("");
>  namebuf << "x#" << i;
>  SCIP_CALL_EXC(SCIPcreateVar(scip, & var, namebuf.str().c_str(),
> 0.0,NULL, ObjCoeff[i], SCIP_VARTYPE_CONTINUOUS, TRUE, FALSE, NULL, NULL,
> NULL, NULL, NULL));
>  SCIP_CALL_EXC(SCIPaddVar(scip, var));
>  _vars.push_back(var);
>  }
>
>
>  Also for adding constraints, I initially set number of nonzero variables
> to 0, and index and values of coefficients as NULL. After that,
> I add coefficients using SCIPaddCoefLinear. Is this correct?
>
>  /* first constraint (flow balancing) in MCF */
>
>
>  j=1;s=1;
> for ( commodity=1, shift = 0 ;  commodity<= K && shift < K;  commodity++,
> shift++)
> {
>  for (n=1; n<=N; n++)
>  {
>  SCIP_CONS * cons;
>       namebuf.str("");
>     namebuf<<"constraint_"<<s;
>  // this is an equality constraint, hence lower and upper bounds are b[s]
>       SCIP_CALL_EXC( SCIPcreateConsLinear(scip, & cons,
> namebuf.str().c_str(), 0, NULL, NULL, b[s], b[s],
>  TRUE, TRUE, TRUE, TRUE, TRUE, FALSE, FALSE, FALSE, FALSE, FALSE) );
>   for(i=1;i<=A;i++)
>  {
>  if(n == Arcs[i][j])
>  { SCIP_CALL_EXC( SCIPaddCoefLinear(scip, cons, _vars[i*K - shift], 1.0)
> ); }
>
>  else if(n == Arcs[i][j+1])
>  { SCIP_CALL_EXC( SCIPaddCoefLinear(scip, cons, _vars[i*K - shift], -1.0)
> );}
>  }
>
>  SCIP_CALL_EXC( SCIPaddCons(scip, cons) );
>  _cons.push_back(cons);
>  s++;
>  }
> }
>
>
>  Please suggest if anything is wrong.
>
>  --
> Thanks with Best Regards,
> Sheetal
>
>
>
> _______________________________________________
> Scip mailing listScip at zib.dehttp://listserv.zib.de/mailman/listinfo/scip
>
>
>


-- 
Thanks with Best Regards,
Sheetal

:)
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