Containers and Reproducibility in Scientific Research

Numerical reproducibility has received increased emphasis in the scientific community. One reason that makes scientific research difficult to repeat is that different computing platforms calculate mathematical operations differently. Software containers have been shown to improve reproducibility in some instances and provide a convenient way to deploy applications in a variety of computing environments. However, there are software patterns or idioms that produce inconsistent results because mathematical operations are performed in different orders in different environments resulting in reproducibility errors. The performance of software in containers and the performance of software that improves numeric reproducibility may be of concern for some scientists. An existing algorithm for reproducible sum reduction was implemented, the runtime performance of this implementation was found to be between 0.3x and 0.5x the speed of the non-reproducible sum reduction. Finally, to evaluate the impact of using a container on performance, the runtime performance of the WRF (Weather Research Forecasting) package was tested and found to be 0.98x of the performance in a native Linux environment

Recovering numerical reproducibility in hydrodynamic simulations

International audienceHPC simulations suffer from failures of numerical reproducibility because of floating-point arithmetic peculiarities. Different computing distributions of a parallel computation may yield different numerical results. We are interested in a finite element computation of hydrodynamic simulations within the openTelemac software where parallelism is provided by domain decomposition. One main task in a finite element simulation consists in building one large linear system and to solve it. Here the building step relies on element-by-element storage mode and the solving step applies the conjugated gradient algorithm. The subdomain parallelism is merged within these steps. We study why reproducibility fails in this process and which operations have to be corrected. We detail how to use compensation techniques to compute a numerically reproducible resolution. We illustrate this approach presenting the reproducible version of hydrodynamic simulations for one test cases provided with the openTelemac software suite