CPXXdualwrite and CPXdualwrite

The routine CPXXdualwrite/CPXdualwrite writes a dual formulation of the current CPLEX problem object.

int CPXXdualwrite( CPXCENVptr env, CPXCLPptr lp, char const * filename_str, double * objshift_p )

int CPXdualwrite( CPXCENVptr env, CPXCLPptr lp, char const * filename_str, double * objshift_p )

Description

The routine CPXXdualwrite/CPXdualwrite writes a dual formulation of the current CPLEX problem object. MPS format is used. This function can only be applied to a linear program; it generates an error for other problem types.

Note: Any fixed variables in the primal are removed before the dual problem is written to a file. Each fixed variable with a nonzero objective coefficient causes the objective value to shift. As a result, if fixed variables are present, the optimal objective obtained from solving the dual problem created using CPXXdualwrite/CPXdualwrite may not be the same as the optimal objective of the primal problem. The argument objshift_p can be used to reconcile this difference.

Arguments

env: A pointer to the CPLEX environment as returned by CPXXopenCPLEX/CPXopenCPLEX.
lp: A pointer to a CPLEX problem object as returned by CPXXcreateprob/CPXcreateprob.
filename_str: A character string containing the name of the file to which the dual problem should be written.
objshift_p: A pointer to a variable of type double to hold the change in the objective function resulting from the removal of fixed variables in the primal.

Return

The routine returns 0 (zero) if successful and nonzero if an error occurs.

Example


status = CPXdualwrite (env, lp, "myfile.dua", &objshift);