Use of the class algorithm

The algorithm class represents a generic optimization algorithm. The user codes the details of such an algorithm in a separate class (the user-defined algorithm, or UDA) which is then passed to algorithm that provides a single unified interface.

Note

The User Defined Algorithms (UDAs) are optimization algorithms (coded by the user) that can be used to build a pygmo object of type algorithm

Some UDAs (optimization algorithms) are already provided with pygmo and we refer to them as pygmo UDAs.

For the purpose of this tutorial we are going to use a pygmo UDA called cmaes to show the basic construction of an algorithm, but the same logic would also apply to a custom UDAs, that is a UDA that is actually coded by the user.

Let us start:

>>> import pygmo as pg
>>> algo = pg.algorithm(pg.cmaes(gen = 100, sigma0=0.3))
>>> print(algo) 
Algorithm name: CMA-ES: Covariance Matrix Adaptation Evolutionary Strategy [stochastic]
    C++ class name: ...
    Thread safety: basic

Extra info:
    Generations: 100
    cc: auto
    cs: auto
    c1: auto
    cmu: auto
    sigma0: 0.3
    Stopping xtol: 1e-06
    Stopping ftol: 1e-06
    Memory: false
    Verbosity: 0
    Force bounds: false
    Seed: ...

In the code above, after the trivial import of the pygmo package, we define a variable algo by constructing an algorithm from cmaes, our implementation of the Covariance Matrix Adaptation Evolutionary Strategy. To construct the pygmo UDA we also pass some parameters (gen and sigma0) whose meaning is documented in cmaes. In the following line we inspect the algorithm. We can see, at a glance, the name of the algorithm and some extra info that indicate the user (in this case us), has implemented, in the UDA (in this case cmaes), the optional method get_extra_info() that prints to screen some fundamental parameters defining the UDA.

We may also get access to the UDA, and thus to its methods not exposed in the algorithm interface, at any time via the extract method:

>>> uda = algo.extract(pg.cmaes)
>>> type(uda)
<class 'pygmo.core.cmaes'>
>>> uda = algo.extract(pg.de)
>>> uda is None
True

Such an extraction will only work if the correct UDA type is passed as argument.