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Command Line Interface

For standalone usage, FeynGraph includes a command line utility called feyngraph. This utility is mostly intended for quick prototyping and backwards compatibility with older diagram generators, and is therefore kept relatively simple.

Installation

The feyngraph command line utility is automatically installed with the FeynGraph library, it requires some additional Python packages though. They are listed in the cli feature and can therefore be installed with 

pip install feyngraph[cli]

Basic Usage

The feyngraph CLI utility requires a configuration file (see Configuration Options) and generates a single output file from the given specification. The output is rendered through a Jinja2 Template, which can be either specified with the --template option or in the config file. The template receives a single object, the DiagramContainer diags containing all diagrams for the given specification. One template is included with FeynGraph, json.jinja to render the diagrams in JSON format. This is also the default output format if no template is given.

Configuration Options

feyngraph expects a single config file in TOML format. A full example configuration using all available options reads 

template = "json.jinja"

[process]
incoming = ["u", "u~"]
outgoing = ["g", "g"]
loops = 2
model = "models/Standard_Model_UFO"
momenta = ["p1", "p2", "k1", "k2", "l1", "l2"]

[filter]
onshell = true
self_loops = 0
opi_components = 1
coupling_orders = { "QCD" = 2, "EW" = 0 }
custom_function = "filter"
custom_code = """
def filter(d: fg.Diagram) -> bool:
    return any(
        sum(p.id() < d.n_ext() for p in v.propagators()) >= 2 for v in d.vertices()
    )

return filter
"""

[drawing]
format = "svg"
outdir = "tmp"
filename = "d_{i}"
The only global option is template, which specifies the path to the Jinja template the output is rendered with. Note that this option is overwritten by the --template command line option if it is set.

Process Specification

The physical process is specified in the [process] table. The possible options are

  • incoming: List of incoming particles, specified as list of the particle names.
  • outgoing: List of outgoing particles, specified as list of the particle names.
  • loops: Number of loops in the generated diagrams.
  • model[optional]: Path to the requested model. Can be the folder of a UFO model or the file of a QGRAF model. Defaults to the Standard Model in Feynman gauge if not specified.
  • momenta[optional]: List of momentum labels to use in the output. Defaults to p<i> for external momenta and l<i> for loop momenta.

Diagram Filters

Several options are available to restrict the set of generated diagrams, they are specified in the [filter] table.

  • onshell: If true, keep only diagrams for which the external legs are on-shell. This is equivalent to removing all diagrams with an internal propagator carrying a single external momentum.
  • self_loops: Keep only diagrams with the specified number of self-loops, i.e. propagators starting and ending at the same vertex.
  • coupling_orders: Keep only diagrams with the given power in the respective coupling. Multiple couplings can be specified.

Additionally, since the feyngraph utility is just a small wrapper around the FeynGraph Python interface, arbitrary filters are also possible. Arbitrary Python code can be passed with the custom_code property, the name of the custom filter function can then be set with the custom_function property. This is expected to be a function taking a single Diagram as input and returning a bool as output.

Warning

The custom filter option can run arbitrary code through the Python interpreter, so make sure to only use filters from trusted sources.

Diagram Drawing

The generated diagrams can also be automatically drawn, this feature is active if the [drawing] table is included in the config. One output file is created for every diagram. The format can be chosen through the options

  • format: Format of the drawing output. Supported values are svg and tikz. The default is svg.
  • outdir: Directory to put the drawings in. Default is feyngraph_drawings.
  • filename: Filename template for the output files. The given string is processed with the str.format() method, which receives the single input i, the identifier of the diagram. The appropriate file ending is appended automatically.