nessai-bilby

Interface and plugin for using nessai in bilby.

This plugin provides two samplers that can be used in bilby:

• nessai: the standard nested sampler from nessai
• inessai: the importance nested sampler from nessai

It also provides a means to use bilby likelihoods and priors directly in nessai, see using bilby likelihoods in nessai

Installation

The package can be installed using pip

pip install nessai-bilby

or conda

conda install conda-forge::nessai-bilby

However, we recommend following installing PyTorch manually to ensure the correct device support.

Note: this plugin requires "bilby>=2.3.0".

Usage

In bilby

One nessai-bilby is installed, both samplers can be used directly in bilby via the run_sampler function. See the bilby documentation for more details on how to run different samplers.

Using bilby likelihoods in nessai

nessai-bilby also provides two model classes that allow bilby likelihood and priors to be used directly with nessai:

• nessai_bilby.model.BilbyModel:
• nessai_bilby.model.BilbyModelLikelihoodConstraint:

Either model can be used by creating an instance of the model and running nessai as usual:

from nessai.flowsampler import FlowSampler
from nessai_bilby.model import BilbyModel

likelihood = ...    # bilby likelihood object
priors = ... # bilby PriorDict

model = BilbyModel(
    priors=priors,
    likelihood=likelihood,
    use_ratio=True    # Whether to use the log-likelihood ratio
)

fs = FlowSampler(
    model,
    ...,
)

fs.run()

Citing

If you use nessai-bilby, please cite the nessai and bilby code bases and the corresponding papers.