The cosmological simulation code $\scriptstyle{\rm CO}N{\rm CEPT}\, 1.0$
  We present version 1.0 of the cosmological simulation code $\scriptstyle{\rm
CO}N{\rm CEPT}$, designed for simulations of large-scale structure formation.
$\scriptstyle{\rm CO}N{\rm CEPT}\, 1.0$ contains a P$^3$M gravity solver, with
the short-range part implemented using a novel (sub)tiling strategy, coupled
with individual and adaptive particle time-stepping. In addition to this,
$\scriptstyle{\rm CO}N{\rm CEPT}$ contains a (linear or non-linear) fluid
solver to treat non-baryonic components which are not easily treatable using
the particle implementation. This allows e.g. for the inclusion of non-linear
massive neutrinos (which may be relativistic) and for simulations that are
consistent with general relativistic perturbation theory. Decaying dark matter
scenarios are also fully supported. A primary objective of $\scriptstyle{\rm
CO}N{\rm CEPT}$ is ease of use. To this end, it has built-in initial condition
generation and can produce output in the form of snapshots, power spectra and
direct visualisations. It also comes with a robust installation script and
thorough documentation. $\scriptstyle{\rm CO}N{\rm CEPT}$ is the first
massively parallel cosmological simulation code written in Python. Despite of
this, excellent performance is obtained, even comparing favourably to other
codes such as $\scriptstyle{\rm GADGET}$ at similar precision, in the case of
low to moderate clustering. We find extraordinary good agreement between
results produced using $\scriptstyle{\rm CO}N{\rm CEPT}\, 1.0$ and
$\scriptstyle{\rm GADGET}$, at all scales and times. The $\scriptstyle{\rm
CO}N{\rm CEPT}$ code itself along with documentation is openly released at
https://github.com/jmd-dk/concept .
