Commit 80c82434 authored by Sam Thiriot's avatar Sam Thiriot
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# Test Functions for NSGA2
# Genetic Algos Visualizations based on R
## Why Test?
## Motivation
Metaheuristics for optimization such as genetic algorithms leave a huge freedom to developers for their implementation.
Genetic Algorithms such as NSGA2 are even less trivial.
Their implementation in the [mgo](https://github.com/openmole/mgo) used in [OpenMole](https://openmole.org/) was adapted so they are efficient for computation on clusters or grids.
This leaves a lot of uncertainty to the user on what really happens.
Why should you, as a user, trust this implementation?
The answer is simple: you should not.
Any implementation in scientific computing should be verified to be trusted.
When using [Genetic Algorithms in OpenMole](https://next.openmole.org/Genetic+Algorithms.html) for calibration or optimization, it is important for the user to understand what happens over time.
Graphing the evolution of evolutionary methods is also necessary for communication.
Basic OpenMole features include the exportation of the populations during the evolution as CSV files.
The web interface of OpenMOLE also helps you to plot these CSV files easily in the user interface.
## Test Functions
A simple way for an user to create graphs is to use the [RTask](https://next.openmole.org/R.html) which enables the usage of R
from OpenMOLE. The first execution of such a task is slow, because OpenMOLE has to download data from the web and build a local container
with the necessary programs. But later executions reuse the same container and are quicker.
Many functions named "Test Functions" were proposed over time to test and compare multi-objective optimization algorithms.
The [wikipedia page](https://en.wikipedia.org/wiki/Test_functions_for_optimization) lists several of them.
Producing graphs automatically after exploration and simulation experiments is part of the methodological recommandations for reproducible research.
A test function is an function you can use as the problem to optimize, for which the expected results are known.
Test functions might test:
- problems with multiple parameters and multiple objectives
- problems with constraints: a part of the space of solutions can not be computed, so the algorithm should achieve to deal with it
- problems with parts of the space of solution that are tricky to detect, either because they are statistically unlikely to find, or because they are in a part of the space of solutions which is heavily constrained, etc.
The results of a test function are usually compared in both terms of:
- coverage of the Pareto front,
- speed of convergence
## Optimization Problem
To illustrate visualization, we proposed in the [example_of_optimization.oms](./example_of_optimization.oms) a simple function
to optimize, and a simple and quick optimization.
This file is imported in other example workflows.
So any modification you would produce in this file would impact all the other examples.
## Test and Learn
## Plot Last Iteration
Test functions have another role: they constitute a simple example of optimization problem.
As a user, you can also learn to tune the parameters of the genetic algorithm as check when convergence
occurs.
In the
## Test Workflows for OpenMole
We provide here a few examples of test functions which you can open with OpenMole.
- ConstrEx
- CP1
- Schaffer N1
- Schaffer N2
To run a test
- Choose one of the workflows starting with "test function"
- Run the workflow
- Update the view on the left using the "refresh" button
- Download the graph of the last Pareto front, and compare it with the literature (you might use the [wikipedia page](https://en.wikipedia.org/wiki/Test_functions_for_optimization) as a start)
You might then tune the parameters of the optimization algorithm and analyze the results, to understand how to better use the optimization method.
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