[Beowulf] Cheap SDR IB

[Alan Louis Scheinine]

With regard to weather codes.  I looked at a program for
local forecasting.  Just six or eight computational
nodes are used.  The grid of physical data is not very dense
because the initial conditions do not have high spatial resolution.
The consequence is that each subdomain has alot of surface area,
that is, alot of communication.  Moreover, there are many variables,
temperature and pressure for diffusion, momentum and pressure for
convection, humidity and ground conditions.
The typical structure is a simple finite-difference block then
exchange of data, then a finite-difference block on another
group of variables and on and on.  There is no "kernel" of
calculation but rather the code is "flat".  The result is that
alot of time is spent waiting for the exchange of data at the
boundaries of subdomains on different compute nodes.

Best regards,
Alan Scheinine

  Centro di Ricerca, Sviluppo e Studi Superiori in Sardegna
  Center for Advanced Studies, Research, and Development in Sardinia

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