Function SCIPfixVarExact 

pub unsafe extern "C" fn SCIPfixVarExact(
    scip: *mut SCIP,
    var: *mut SCIP_VAR,
    fixedval: *mut SCIP_RATIONAL,
    infeasible: *mut c_uint,
    fixed: *mut c_uint,
) -> SCIP_RETCODE

in problem creation and solving stage, both bounds of the variable are set to the given value; in presolving stage, the variable is converted into a fixed variable, and bounds are changed respectively; conversion into a fixed variable changes the vars array returned from SCIPgetVars() and SCIPgetVarsData(), and also renders arrays returned from the SCIPvarGetImpl…() methods invalid

@return \ref SCIP_OKAY is returned if everything worked. Otherwise a suitable error code is passed. See \ref SCIP_Retcode “SCIP_RETCODE” for a complete list of error codes.

@pre This method can be called if @p scip is in one of the following stages: - \ref SCIP_STAGE_PROBLEM - \ref SCIP_STAGE_PRESOLVING - \ref SCIP_STAGE_SOLVING