# More Samples

## CLP's Samples Directory

The CLP dsitribution includes a number of `.cpp` sample files. Users are encouraged to use them as starting points for their own CLP projects. The files can be found in the `&clpsamplesdir;` directory. For the latest information on compiling and running these samples, please see the file `&clpsamplesdir;INSTALL`. Below is a list of some of the most useful sample files with a short description for each file.

Basic Samples

Source file | Description
--- | ---
&minimumcpp; | This is a CLP "Hello, world" program. It reads a problem from an MPS file, and solves the problem. [More...]
&defaultscpp; | This is one of the simpler driver programs available. It sets tolerances to defaults and is a good place to find straightforward uses of "set" and "get" methods. It also prints out full MPS-like solutions. [More...]
&drivercpp; | This is designed to be a file that a user could modify to get a useful driver program for his or her project. In particular, it demonstrates the use of CLP's presolve functionality. [More...]
&networkcpp; | This shows the use of non-standard matrices and how to load a problem without the use of MPS files. [More...]
&testbarriercpp; | This is a basic driver file for the barrier method of CLP, similar to &minimumcpp;. The barrier method is not currently addressed in this guide. [More...]

Advanced Samples

Source file | Description
--- | ---
&driver2cpp; | This sample, in addition to some tasks common to other samples, does some advanced message handling and presolve.
&dualcutscpp; | This sample implements a method of treating a problem as a collection of cuts.
&decomposecpp; | This does full Dantzig-Wolfe decomposition. It illustrates the use of many models, adding columns, et cetera.
&sprintcpp; | This solves a long, thin problem by solving smaller subsets. It is a simplified version of work done by one of the authors on aircrew scheduling problems. It shows the use of two models and their synchronization. A more general version can be found in `COIN/Clp/ClpSolve.cpp`
&sprint2cpp; | This is similar to `sprint.cpp` but is designed for solving large problems with little choice. The idea is that if relatively few variables are fixed, presolve can greatly reduce the problem size so that a series of solves can get close to the optimal solution much faster than would a naïve solve of the full problem.

The remaining Samples listed here are considered unsupported in that they are of a more esoteric nature and are sometimes contributed as a result of an individual's request. The are to be found in `&clpsamplesdir;Contributed`.

Unsupported Samples

Source file | Description
--- | ---
&testbasiscpp; | This sample takes a problem, changes any inequality constraints to equality constraints, solves the problem, and creates the optimal basis.
&testgubcpp; | This sample illustrates the use of the GUB ("Generalized Upper Bound") technique.
&ekkcpp; | This sample can be used to compare CLP and OSL. It uses an additional file in the Samples directory, `ekk_interface.cpp`. These sample files are not likely to be interesting to new CLP users who do not have experience with OSL.
&hellocpp; | This sample creates a text-based picture of a matrix on screen (limited to an 80x80 matrix). It's not terribly useful but it does illustrate one way to step through the elements of a matrix.
&piececpp; | This sample takes a matrix read in by CoinMpsIo (can be used to read in MPS files without a solver), deletes every second column and solves the resulting problem.
&usevolumecpp; | The Volume Algorithm is another solver available as part of the COIN-OR distribution. This sample shows how to use the Volume Algorithm with CLP.

### minimum.cpp

This sample is examined in more detail in .

### defaults.cpp

This sample begins by reading an MPS file. The default MPS file is `COIN/Mps/Sample/p0033.mps`; this can be over-riden by a command-line specification of a (path and) file name). The sample then sets the pivot algorithm to be exact devex. It "gets" the default infeasibility cost and "sets" it to that value (and prints it to standard out). This sort of getting and setting of various parameters constitutes a common theme in this sample, with the purpose of illustrating usage of some of the more common get and set methods available in CLP.

At this point the model is solved by the primal method. A sequence of sets, gets and prints is then followed by a number of calls to methods which give specific information about the status of the problem (for example, the code checks that the current solution has been proven to be optimal by `assert(model.isProvenOptimal())`).

Next, a copy of the original model is made. More sets and gets are performed to demonstrate the use of additional options (including the setting of the default message handling as well as changing of the "log level" (amount of output)). The model is solved again a number of times between changes of the optimization direction (i.e. changing from min to max or vice versa). The remaining lines of this sample serve to display solution and problem information in much the same way as is done in driver.cpp.

### driver.cpp

This sample begins by reading an MPS file. The default MPS file is `COIN/Mps/Sample/p0033.mps`; this can be over-riden by a command-line specification of a (path and) file name). A second command-line argument can specify that either the "primal" or "dual" method (or even the "barrier", see below) should be used by CLP.

Once the problem has been read, there are two options for how to solve it, one of which must be chosen at compile-time (`STYLE1` being defined or not determines this choice). The second manner is more flexible and involves more specific directions being given to CLP, including the ability to specify that the barrier method should be used.

At this point in the sample, the problem is solved by CLP, and some basic ouput is generated. If more output is desired, at compile-time, an `exit(0)` statement must either be removed or commented. There are two levels of additional output, the first of which is suppressed by a `#if 0` directive which may be modified at compile-time if desired. This first level of output only involves non-zero columns, whereas the second provides additional information.

### network.cpp

This handy sample reads a network problem generated by netgen, converts it to an LP using CLP's network matrix type, and solves. This entirely avoids the use of an MPS file, as the LP is built in memory from the network data file created by netgen. Also, the factorization frequency is changed, and the problem is solved more than once (demonstrating the change of optimization sense as well as switching from dual to primal methods).

### testBarrier.cpp

This straightfoward sample begins by reading a problem from an MPS file. It then chooses a Cholesky factorization and solves the problem using the predictor corrector barrier method. It then copies the problem and performs a crossover to a simplex solution in the new copy.

### dualCuts.cpp

This sample begins with only the equality constraints of a problem. The inequalities are considered to be part of a pool of available cuts in much the same way as is done in integer programming. However, in this case, the cuts are not "generated", they are simply the inequalities of the problem.

### decompose.cpp

More on this sample coming soon!

### driver2.cpp

More on this sample coming soon!

## Common CLP Tasks in the Samples

Below is a listing of a number of common CLP tasks, such as loading a problem from an MPS file, matched with a list of each Sample file which illustrates the performance of a given task.

Contents of the Samples directory

CLP Task(s) | Method(s) | Sample(s)
--- | --- | ---
Read problem from MPS file |
    int readMps(const char *filename)
| &defaultscpp;, &drivercpp;, &minimumcpp;
Solve by primal method |
    int primal()
| &drivercpp;
Choose pivot rule |
    void setPrimalColumnPivotAlgorithm(ClpPrimalColumnPivot &choice)
    	void setDualRowPivotAlgorithm(ClpDualRowPivot &choice)
| &defaultscpp;
Get/set infeasibility cost |
    void setInfeasibilityCost(double value)
    	void setInfeasibilityCost(double value)
| &defaultscpp;
Get string/"double"/integer information |
    bool getStrParam(ClpStrParam key, std::string &value) const
    	bool getDblParam(ClpDblParam key, double &value) const
    	bool  getIntParam (ClpIntParam key, int &value) const
| &defaultscpp;
Set maximum number of iterations |
    void setMaximumIterations(int value)
| &defaultscpp;
Check solution status |
    int status() const
    	bool isAbandoned() const
    	bool isProvenOptimal() const
    	bool isProvenPrimalInfeasible() const
    	bool isProvenDualInfeasible() const
    	bool isPrimalObjectiveLimitReached() const
    	bool isDualObjectiveLimitReached() const
    	bool isIterationLimitReached() const