Solvers
=======

To configure a solver, you must first initialize the Engine with the list of all
the solvers you want to use, and then you must specify the specific solver to
use for each run. Trident will load certain solvers by default:

- COIN-CLP
- IBM Cplex

COIN-CLP
--------

The COIN Linear Programming solver is supported by default and is provided as
part of the Trident python package. It is enabled by default.

To load it explicitly, provide the following parameter to `Engine`:

.. code-block:: python

    engine = Engine(solver_modules=["trident.solver.coin"])

To use the solver in a run, specify in the run config:

.. code-block:: json

    {
        // ...
        "solver": {"name": "coin-clp"}
        // ...
    }

IBM Cplex
---------

Integration with the Cplex solver for solving hydro power optimization problems
is provided by default. The cplex sovler DLL is not provided as part of the
trident python package, and must be provided separately by the user.

To load it explicitly, provide the following parameter to `Engine`:

.. code-block:: python

    engine = Engine(solver_modules=["trident.solver.cplex"])

To use the solver in a run, specify in the run config:

.. code-block:: json

    {
        // ...
        "solver": {"name": "cplex"}
        // ...
    }

Providing the Cplex solver on Windows or Linux
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If the cplex solver DLL is present on your system, you can provide the path to
Trident via the `CPLEX_DLL_PATH` environment variable on Windows, or the
`LD_LIBRARY_PATH` environment variable on Linux.

If IBM Cplex Studio is installed on your system, then Trident will automatically
detect the path to the solver.

Disabling Cplex
^^^^^^^^^^^^^^^

To disable loading of the Cplex solver, there are two options:

- Either: set the `TRIDENT_WITH_CPLEX` enironment variable to `0`.
- Or: explicitly provide the `solver_modules` parameter to `Engine`.

LP solver algorithm
-------------------

You can specify which LP algorithm to use in the run config:

.. code-block:: json

    {
        // ...
        "solver": {
            "name": "cplex",
            "algorithm": "dual_simplex"
        }
        // ...
    }

Supported values are:


- "dual_simplex"
- "barrier"
- "primal_simplex"