Once initial conditions are enabled, the output file named SMASH_IC (followed by the appropriate suffix) is generated when SMASH is executed.
The output is available in Oscar1999, Oscar2013, ASCII, Oscar2013_bin and ROOT format, as well as in an additional "For_vHLLE" format. The latter is meant to directly serve as input for the vHLLE hydrodynamics code Karpenko:2013wva [31].

Human-readable output

In case of the Oscar1999 and Oscar2013 format, the structure is identical to the Oscar Particles format (see OSCAR particles format), and the custom ASCII format is also available.
In contrast to the usual particles output however, the initial conditions output provides a list of all particles removed from the evolution at the time when crossing the hypersurface. This implies that neither the initial particle list nor the particle list at each time step is printed.
The general Oscar structure as described in OSCAR particles format is preserved.

Binary output

The binary initial conditions output also provides a list of all particles removed from the evolution at the time when they cross the hypersurface. For each removed particle a 'p' block is created that stores the particle data.

Only the particle block header differs from the standard binary output structure described in Binary format; the individual particle lines themselves use exactly the same layout as in the regular binary output.

The header has the following structure:

char uint32_t

'p' n_part_lines

Custom particle quantities are also available; their usage is described in Binary format.

ROOT output

The initial conditions output in shape of a list of all particles removed from the SMASH evolution with a "Constant_Tau" fluidization criterion is also available in ROOT format. Neither the initial nor the final particle lists are printed, but the general structure for particle TTrees, as described in ROOT format, is preserved.

Output for vHLLE

The "For_vHLLE" initial conditions output SMASH_IC_For_vHLLE.dat contains a list of particles on a hypersurface of constant proper time. This output is formatted such that it is directly compatible with the vHLLE hydrodynamics code Karpenko:2013wva [31]. As a consequence, spectators are not written to the IC output as they would need to be excluded anyways in order to initialize the hydrodynamics evolution. Note though that for all other output formats the full particle list is printed to the IC output, including spectators. The particle data is provided in the computational frame. For further details, see Initial conditions.
The "For_vHLLE" initial conditions output is formatted as follows:

Header

# **smash_version** initial conditions: hypersurface of constant proper time
# tau x y eta mt px py Rap pdg charge baryon_number strangeness
# fm fm fm none GeV GeV GeV none none e none none

The header consists of 3 lines starting with a '#', containing the following information:

SMASH-version and the information, that 'initial conditions' are provided
The header with all column names
The units of all column quantities

Output block header

The initial conditions output for vHLLE is, similar to the OSCAR output, based on a block structure, where each block consists of 1 event (multiple ensembles, if used, are separated as well). The header for a new event is structured as follows:

# event ev_num ensemble ens_num start

where

ev_num: The number of the current event
ens_num: The number of the current ensemble

Note that 'event', 'ensemble' and 'start' are not variables, but words that are printed in the header.

Particle line

The particle lines are formatted as follows:

tau x y eta mt px py Rap pdg charge baryon_number strangeness

smash::pdg::eta

constexpr int eta

η.

Definition: pdgcode_constants.h:89

where

tau: Proper time of the particle
x, y: Cartesian x and y coordinates of the particle
eta: Space-time rapidity of the particle
mt: Transverse mass of the particle
px, py: x and y components of the particle's momentum
Rap: Momentum space rapidity of the particle
pdg: PDG code of the particle (see http://pdg.lbl.gov/). It contains all quantum numbers and uniquely identifies its type. every particle in the event.
charge: electric charge of the particle
baryon_number: baryon number of the particle
strangeness: strangeness of the particle

Event end line

The end of an event is indicated by the following line:

# event ev_num ensemble ens_num end

where

ev_num: The number of the current event
ens_num: The number of the current ensemble

Note that 'event', 'ensemble' and 'start' are not variables, but words that are printed in the header.

Note: If SMASH is run with test particles (necessary e.g. for potentials), the output will contain Ntest * Npart particle entries. Remember to weigh each of those particles with 1/Ntest.