IloAlgorithm is the base class of algorithms in Concert Technology. An instance of this class represents an algorithm in Concert Technology.

In general terms, you define a model, and Concert Technology extracts objects from it for your target algorithm and then solves for solutions.

Most member functions in this class contain assert statements. For an explanation of the macro NDEBUG (a way to turn on or turn off these assert statements), see the concept Assert and NDEBUG.

Status

The member function getStatus returns a status showing information about the currently extracted model and the solution (if there is one). For explanations of the status, see the nested enumeration IloAlgorithm::Status.

Exceptions

The class IloAlgorithm::Exception, derived from the class IloException, is the base class of exceptions thrown by classes derived from IloAlgorithm. For an explanation of exceptions thrown by instances of IloAlgorithm, see IloAlgorithm::Exception.

Streams and Output

The class IloAlgorithm supports these communication streams:

• ostream& IloAlgorithm::error() const; for error messages.
• ostream& IloAlgorithm::out() const; for general output.
• ostream& IloAlgorithm::warning() const; for warning messages about nonfatal conditions.

Child classes:

• the class IloCplex in the ILOG CPLEX Reference Manual
• the class IloCP in the ILOG CP Optimizer Reference Manual.
• the class IloSolver in the ILOG Solver Reference Manual .

This constructor creates an algorithm in Concert Technology from its implementation object. This is the default constructor.

This member function clears the current model from the algorithm.

This member function deletes the invoking algorithm. That is, it frees memory associated with the invoking algorithm.

This member function returns a reference to the stream currently used for error messages from the invoking algorithm. IloAlgorithm::error is initialized with the value of IloEnv::error.

This member function extracts the extractable objects from a model into the invoking algorithm if a member function exists to extract the objects from the model for the invoking algorithm. Not all extractable objects can be extracted by all algorithms; see the documentation of the algorithm class you are using for a list of extractable classes it supports.

When you use this member function to extract extractable objects from a model, it extracts all the elements of that model for which Concert Technology creates the representation of the extractable object suitable for the invoking algorithm.

The attempt to extract may fail. In case such a failure occurs, Concert Technology throws the exception CannotExtractException on platforms that support C++ exceptions when exceptions are enabled.

For example, a failure will occur if you attempt to extract more than one objective for an invoking algorithm that accepts only one objective, and Concert Technology will throw the exception MultipleObjException.

This member function returns the environment of the invoking algorithm.

This member function returns the integer value of an integer variable in the current solution of the invoking algorithm. For example, to access the variable, use the member function getIntValue(var) where var is an instance of the class IloIntVar.

If there is no value to return for var, this member function raises an error. This member function throws the exception NotExtractedException if there is no value to return (for example, if var was not extracted by the invoking algorithm).

This member function accepts an array of variables vars and puts the corresponding values into the array vals; the corresponding values come from the current solution of the invoking algorithm. The array vals must be a clean, empty array when you pass it to this member function.

If there are no values to return for vars, this member function raises an error. On platforms that support C++ exceptions, when exceptions are enabled, this member function throws the exception NotExtractedException in such a case.

This member function returns the model of the invoking algorithm.

This member function returns the numeric value of the objective function associated with the invoking algorithm.

This member function returns a status showing information about the current model and the solution. For explanations of the status, see the nested enumeration IloAlgorithm::Status.

This member function returns the amount of time elapsed in seconds since the most recent reset of the invoking algorithm. (The member function IloAlgorithm::printTime directs the output of getTime to the output channel of the invoking algorithm.)

This member function returns the value of an expression in the current solution of the invoking algorithm. For example, to access the expression, use the member function getValue(expr) where expr is an instance of the class IloNumExprArg.

If there is no value to return for expr, this member function raises an error. This member function throws the exception NotExtractedException if there is no value to return (for example, if expr was not extracted by the invoking algorithm).

This member function returns the value of an objective in the current solution of the invoking algorithm. For example, to access the objective, use the member function getValue(obj) where obj is an instance of the class IloObjective.

If there is no value to return for obj, this member function raises an error. This member function throws the exception NotExtractedException if there is no value to return (for example, if obj was not extracted by the invoking algorithm).

This member function returns the numeric value of an integer variable in the current solution of the invoking algorithm. For example, to access the variable, use the member function getValue(var) where var is an instance of the class IloIntVar.

If there is no value to return for var, this member function raises an error. This member function throws the exception NotExtractedException if there is no value to return (for example, if var was not extracted by the invoking algorithm).

This member function returns the numeric value of a numeric variable in the current solution of the invoking algorithm. For example, to access the value of the variable, use the member function getValue(var) where var is an instance of the class IloNumVar.

If there is no value to return for var, this member function raises an error. This member function throws the exception NotExtractedException if there is no value to return (for example, if var was not extracted by the invoking algorithm).

This member function accepts an array of variables vars and puts the corresponding values into the array vals; the corresponding values come from the current solution of the invoking algorithm. The array vals must be a clean, empty array when you pass it to this member function.

If there are no values to return for vars, this member function raises an error. On platforms that support C++ exceptions, when exceptions are enabled, this member function throws the exception NotExtractedException in such a case.

This member function accepts an array of variables vars and puts the corresponding values into the array vals; the corresponding values come from the current solution of the invoking algorithm. The array vals must be a clean, empty array when you pass it to this member function.

If there are no values to return for vars, this member function raises an error. On platforms that support C++ exceptions, when exceptions are enabled, this member function throws the exception NotExtractedException in such a case.

This member function returns IloTrue if extr has been extracted for the invoking algorithm; otherwise, it returns IloFalse.

This member function returns a reference to the stream currently used for logging. General output from the invoking algorithm is accessible through this member function. IloAlgorithm::out is initialized with the value of IloEnv::out.

This member function directs the output of the member function IloAlgorithm::getTime to an output channel of the invoking algorithm. (The member function IloAlgorithm::getTime accesses the elapsed time in seconds since the most recent reset of the invoking algorithm.)

This member function resets the timer on the invoking algorithm. The type of timer is platform dependent. On Windows systems, the time is elapsed wall clock time. On UNIX systems, the time is CPU time.

This member function sets the stream for errors generated by the invoking algorithm. By default, the stream is defined by an instance of IloEnv as cerr.

This member function redirects the out() stream with the stream given as an argument.

This member function can be used with IloEnv::getNullStream to suppress screen output by redirecting it to the null stream.

This member function sets the stream for warnings from the invoking algorithm. By default, the stream is defined by an instance of IloEnv as cout.

This member function solves the current model in the invoking algorithm. In other words, solve works with all extractable objects extracted from the model for the algorithm. The member function returns IloTrue if it finds a solution (not necessarily an optimal one). Here is an example of its use:

 if (algo.solve()) {
   algo.out() << "Status is " << algo.getStatus() << endl;
 };

If an objective of the model has been extracted into the invoking algorithm, this member function solves the model to optimality. If there is currently no objective, this member function searches for the first feasible solution. A feasible solution is not necessarily optimal, though it satisfies all constraints.

This member function returns a reference to the stream currently used for warnings from the invoking algorithm. IloAlgorithm::warning is initialized with the value of IloEnv::warning.

IloAlgorithm is the base class of algorithms in Concert Technology, and IloAlgorithm::Status is an enumeration limited in scope to the class IloAlgorithm. The member function IloAlgorithm::getStatus returns a status showing information about the current model and the solution.

Unknown specifies that the algorithm has no information about the solution of the model.

Feasible specifies that the algorithm found a feasible solution (that is, an assignment of values to variables that satisfies the constraints of the model, though it may not necessarily be optimal). The member functions IloAlgorithm::getValue access this feasible solution.

Optimal specifies that the algorithm found an optimal solution (that is, an assignment of values to variables that satisfies all the constraints of the model and that is proved optimal with respect to the objective of the model). The member functions IloAlgorithm::getValue access this optimal solution.

Infeasible specifies that the algorithm proved the model infeasible; that is, it is not possible to find an assignment of values to variables satisfying all the constraints in the model.

Unbounded specifies that the algorithm proved the model unbounded.

InfeasibleOrUnbounded specifies that the model is infeasible or unbounded.

Error specifies that an error occurred and, on platforms that support exceptions, that an exception has been thrown.

See Also the enumeration IloCplex::Status in the ILOG CPLEX Reference Manual for status specific to the CPLEX algorithms.