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SWIFT
SWIFTweb
Commits
830d0cee
Commit
830d0cee
authored
7 years ago
by
Josh Borrow
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Minor typo fixes
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!11
Updated homepage text for all 3 sections
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data/astro.md
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data/cs.md
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@@ -7,13 +7,13 @@ directly be read by SWIFT. The only difference is the parameter file
that will need to be adapted for SWIFT.
SWIFT combines multiple numerical methods that are briefly outlined
here. The whole art is to efficiently couple them to
efficiently
here. The whole art is to efficiently couple them to
exploit modern computer architectures.
## Gravity
SWIFT uses the Fast Multipole Method (FMM) to calculate gravitational
forces between near
-
by particles. These forces are combined with
forces between nearby particles. These forces are combined with
long-range forces provided by a mesh that captures both the periodic
nature of the calculation and the expansion of the simulated universe.
SWIFT currently uses a single fixed but time-variable softening length
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@@ -32,7 +32,7 @@ frequency of the update.
SWIFT implements a standard LCDM cosmology background expansion and
solves the equations in a comoving frame. We allow for equations of
state of dark-energy that evolve
s
with scale-factor. The structure of
state of dark-energy that evolve with scale-factor. The structure of
the code can easily allow for modified-gravity solvers or
self-interacting dark matter schemes to be implemented. These will be
part of future releases of the code.
...
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@@ -64,12 +64,12 @@ can be written with no viscosity switches nor thermal diffusion
terms. It follows exactly the description in the review of the topic
by
[
Price 2012
](
http://adsabs.harvard.edu/abs/2012JCoPh.231..759P
)
and
is not optimised. This mode is used for education purposes or can
serve as
the
basis to help developers create other hydrodynamics
serve as
a
basis to help developers create other hydrodynamics
schemes.
### GADGET-2 SPH
SWIFT
make
s a 'backwards-compatible'
[
GADGET-2
SWIFT
contain
s a 'backwards-compatible'
[
GADGET-2
SPH
](
http://adsabs.harvard.edu/abs/2002MNRAS.333..649S
)
mode, which
uses a standard
[
Monaghan
1977
](
http://adsabs.harvard.edu/abs/1977MNRAS.181..375G
)
artificial
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@@ -87,11 +87,10 @@ schemes from [Hopkins
available for use. These schemes use a weighting factor of either
entropy or energy in the calculation of density, which has the effect
of promoting mixing and reducing spurious surface tensions that are
present in a traditional "Density-Entropy" scheme (such as the
GADGET-2 one presented above). This scheme avoids artificial surface
tension at contact discontinuities and allows for better mixing
between phases. This leads to a much better behaviour of the SPH
method in cases such at the Kelvin-Helmholtz instabilities or the
present in a traditional "Density-Entropy" scheme (such as the GADGET-2 one
presented above). This scheme avoids artificial surface tension at contact
discontinuities and allows for better mixing between phases. This leads to much
better behaviour in cases such at the Kelvin-Helmholtz instabilities or the
infamous
[
'blob'
test
](
http://adsabs.harvard.edu/abs/2007MNRAS.380..963A
)
.
...
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@@ -99,9 +98,9 @@ test](http://adsabs.harvard.edu/abs/2007MNRAS.380..963A).
SWIFT can also use the GIZMO scheme (
[
Hopkins
2015
](
http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1409.7395
)
),
also know as 'SPH-ALE' outside of astrophysics. This scheme
s
is a
also know as 'SPH-ALE' outside of astrophysics. This scheme is a
hybrid between a particle method and a finite volume method. Whilst
particles are
being
used to represent the fluid, fluxes between them
particles are used to represent the fluid, fluxes between them
are computed and exchanged using Riemann solvers and proper gradient
reconstruction. This allows for a much more accurate representation of
the physics without any ad-hoc switches for viscosity or thermal
...
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@@ -150,7 +149,7 @@ project](http://adsabs.harvard.edu/abs/2014ApJS..210...14K).
SWIFT can be linked to the VELOCIraptor phase-space structure finder
to return haloes and sub-haloes while the simulation is running. This
on-the-fly processing allows for a much faster time-to-science than in
the classic
way
of post-processing simulations after they are run.
the classic
method
of post-processing simulations after they are run.
## Documentation and tests
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modified version of the publicly available lightweight tasking library
[
QuickShed
](
https://gitlab.cosma.dur.ac.uk/swift/quicksched
)
as its
backbone. Communications between compute nodes are scheduled by the
library itself and use asynchronous call to MPI to maximise the
library itself and use asynchronous call
s
to MPI to maximise the
overlap between communication and computation. The domain
decomposition itself is performed by splitting the graph of all the
compute tasks, using the METIS library,
such as
to minimise the number
of required MPI communications. The core calculations in SWIFT use
d
compute tasks, using the METIS library, to minimise the number
of required MPI communications. The core calculations in SWIFT use
hand-written SIMD intrinsics to process multiple particles in parallel
and achieve maximal performance.
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@@ -40,6 +40,6 @@ and where most other codes struggle to harvest any scaling or performance.
## I/O performance
SWIFT uses the parallel-hdf5 library to read and write snapshots
efficiently on distributed file systems.
By
careful tuning of
the
efficiently on distributed file systems.
Through
careful tuning of
Lustre parameters, SWIFT can write snapshots at the maximal disk
writing speed of a given system.
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## What is SPH?
Smoothed Particle Hydrodynamics (SPH) is a numeric
l
a method
o
f
Smoothed Particle Hydrodynamics (SPH) is a numerica
l
method f
or
approximating the forces between fluid elements (gas or
liquids). Let's say that we want to simulate some water and a wave
within it. Even a singl
l
e liter of water has
within it. Even a single liter of water has
100000000000000000000000000 particles in it. To store that much data
we would require a computer that as 100 trillion times as much storage
space as
*all of the data on the internet*
. It's clear that we need a
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