After returning back from the NSF Workshop Archiving Experiments to Raise Scientific Standards, here are some thoughts on reproducible research. Thanks to Dan Gezelter, Dennis Shasha, and others for inspiring discussions.

First of all, it is important to point out that reproducibility is not the goal in itself. There are many situations in which strict computational reproducibility is not achievable. The goal is an exposure of the scientific communication to a skeptic inquiry. A mathematical proof is an example of a scientific communication, which is constructed as a dialogue with a skeptic: someone who might say “What if your conclusions are not true?” Step by step, a mathematical proof is designed to convince the skeptic that the conclusion (a theorem) has to be true. As for computational results, even the simplest skeptic inquiry “What if there is a bug in your code?” cannot be answered unless the software code and every computational step that led to the published result are open for inspection.

If you attend a mathematical conference, you can notice that mathematicians do not usually go through every step in the proof to present a theorem, it is enough to sketch the main idea of the proof. However, the audience understands that the detailed proof should be available in the published work, otherwise the theorem cannot be accepted. Similarly, in a presentation of a computational work, one can simply show results of a computational experiment. However, such results cannot be accepted as scientific unless the full computation is disclosed for a skeptic inquiry. As stated by Dave Donoho (who paraphrased Jon Claerbout),

An article about computational science in a scientific publication is not the scholarship itself, it is merely advertising of the scholarship. The actual scholarship is the complete software development environment and the complete set of instructions which generated the figures.

If you don’t want to disclose the details of your computation, then the work that you do is not science. As for reproducibility, there seems to be different degrees of it:

1. Replicability: the ability to reproduce the computation as published
2. Reusability: the ability to apply a similar algorithm to a different problem or different input data
3. Reconfigurability: the ability to obtain a similar result when the parameters of the experiment are perturbed deliberately

Some algorithms are perfectly replicable but of limited use, because they are too sensitive to the choice of parameters to be reusable or reconfigurable. Nevertheless, such algorithms deserve a place in the scientific body of knowledge, because they may lead to a discovery or invention of more robust algorithms.

Those who read Italian may enjoy the philosophical article on open software and reproducible research by Alessandro Frigeri and Gisella Speranza: “Eppur si muove” Software libero e ricerca riproducibile Eppur si muove (and yet it moves) are the words attributed to Galileo Galilei, the father of modern science.