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Checking the floating point accuracy of scientific codes by using the verificarlo tool

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 Christophe Denis
Le mardi 19 avril 2016 à 11:00
Salle de Conférence (Pavillon des Jardins)
Christophe Denis (CMLA, ENS Cachan)

In the next decade, exascale supercomputers will provide the computational power required to perform very large scale simulations. For certain applications the results of exascale simulations will be of such high reslution that experimental measurements will be insufficient for validation purposes. As floating point approximations of numeric expressions are neither associative nor distributive, the results of a numerical simulation can differ between executions. As reported by the numerician I. S. Duff, "Getting different results for different runs of the same computation can be disconcerting for users even if, in a sense, both results are correct". There is a need to have an automatic and global approach giving a confidence interval on the results taking into account the floating point arithmetic effect. The estimation of the effect of the floating point model on the accuracy of the computed results is the first step of a rigorous Verification and Validation (V&V) procedure.

This talk is organised as follows. The context of our work and in particular the dark side of the floating point computation is firstly presented. A brief overview of some numerical verification tools is the reported. Then, the new tool called verificarlo is exposed. Using verificarlo is transparent for the user and does not require manually modifying the source code. It can be used for the automatic assessment of the numerical accuracy of large scale digital simulations by using the Monte-Carlo Arithmetic. Several examples will be displayed in particular the numerical verification of the solving of linear systems using the LAPACK and BLAS scientific libraries.

More information about the verificarlo tool could be obtained here: https://hal.archives-ouvertes.fr/hal-01192668

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mar. 19 février

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