<div dir="ltr">Hi,<br><br><div class="gmail_quote"><div dir="ltr">On Tue, Jul 31, 2018 at 6:14 AM Theodore Omtzigt <<a href="mailto:theo@stillwater-sc.com">theo@stillwater-sc.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Dear Devs:<div><br></div><div><br clear="all"><div><div class="m_-1125029773112752487gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div>I am trying to connect with the current developers/maintainers of the GROMACS code. We have been working with a large international consortium of computational scientists on a new number system, called posits, to replace IEEE floating point with a high-performance reproducible tapered floating point format with higher numerical accuracy. </div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></blockquote><div><br></div><div>That sounds interesting, but I suspect there is not currently a compelling advantage for molecular dynamics applications. Fidelity in computation is not known to be a dominant source of error in the simulations, whereas doubts about the accuracy of the model physics ("force field") and the limitations created by finite sampling are well known. And the latter implies a strong need to use the fastest form of computation that can implement models that can be shown to be consistent with real physics. If a change of representation facilitated the evaluation of a 1/sqrt(x) function that on commodity hardware had an execution time similar to multiplication, then that would be interesting. But without hardware support, the impact of such an implementation for GROMACS users would be zero.</div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div><div class="m_-1125029773112752487gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div>One of our supercomputer center customers want to enable GROMACS with this new number system, and I am looking for subject matter experts that we should work with to enable GROMACS with the C++ posit arithmetic library that has been developed for the posit-based hardware accelerators.</div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></blockquote><div><br></div><div>What advantage has that center identified?</div><div><br></div><div>There are "plain C" versions of the various numerical kernels that are already available to be the basis for such efforts. So it would "simply" be a matter of converting from IEEE to posit before entering the main loop and calling those kernels within the loop. Early implementations should only consider doing the force computation in posit representation.</div><div><br></div><div>Mark</div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div><div class="m_-1125029773112752487gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div>Looking forward to connecting with the computational kernel SMEs of GROMACS.</div><div><br></div><div>With warm regards,</div><div><br></div><div>Theodore Omtzigt</div></div></div></div></div></div></div></div></div></div></div></div><div><div dir="ltr"><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div><br></div></div></div></div></div></div></div></div></div></div></div></div></div>
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