Output

GEMC writes simulation data through gstreamer plugins. Each plugin serializes the event, run, and frame data produced during a simulation run into a specific file format.

One or more outputs are configured with the gstreamer YAML key:

gstreamer:
  - format: csv
    filename: myrun
  - format: root
    filename: myrun

Multiple entries are allowed; GEMC instantiates all configured plugins in parallel.

Built-in formats

Format	Type token	Extension	Best for
ASCII	`ascii`	`.txt`	Inspection, debugging
CSV	`csv`	`.csv`	Python / pandas analysis
JSON	`json`	`.json`	Web tools, streaming pipelines
ROOT	`root`	`.root`	HEP analysis with ROOT TTrees
JLAB SRO	`jlabsro`	`.ev`	Jefferson Lab streaming readout frames
HIPO	`hipo`	`.hipo`	CLAS12 analysis with standard banks

HIPO is a separately installed plugin specific to the CLAS12 detector suite. The remaining formats are bundled with GEMC.

Output types

The type sub-key selects what the plugin writes:

Type	Content
`event` (default)	per-event hits: headers, true info, digitized data, generated particles
`stream`	per-frame time-snapshot payloads

gstreamer:
  - format: root
    filename: myrun
    type: event       # default
  - format: jlabsro
    filename: myrun
    type: stream      # frame snapshots

Threading and file naming

Event-based outputs (such as flux or custom plugins) produce one file per worker thread. The thread index is appended to the filename automatically:

myrun_t0.root   myrun_t1.root   myrun_t2.root   ...

Run-based outputs (such as dosimeter) accumulate across the full run and produce a single file per streamer:

myrun.root

The number of threads is controlled by nthreads. A value of 0 (the default) uses one thread per available core.

Event buffer

Each streamer instance accumulates events in memory and flushes them to disk in batches. The default batch size is 100 events. Adjust it with ebuffer:

ebuffer: 50

Smaller values reduce peak memory use at the cost of more frequent I/O.

Writing a custom plugin

When the built-in formats are not enough, you can ship your own output plugin as a .gplugin shared library. See Writing an output plugin for a step-by-step guide.