AletheiaCosmo 0.1.1

An emulator of the non-linear matter power spectrum based on the evolution mapping approach.

Aletheia

Author	Ariel Sánchez and The Aletheia Team
Contributors	Ariel Sánchez, Andres Ruiz, Facundo Rodriguez, Carlos Correa, Andrea Fiorilli, Matteo Esposito, Jenny Gonzalez Jara, Nelson D. Padilla
Source	Source code at GitLab
Documentation	Documentation at MPCDF Pages
Installation	pip install AletheiaCosmo
Reference	Sánchez et al. (2025, in prep)

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Aletheia is an accurate and robust Python package that provides emulated predictions for the non-linear matter power spectrum.

At its core, Aletheia is based on the evolution mapping framework, which provides a high degree of flexibility and allows the emulator to cover a wide cosmology parameter space at continuous redshifts up to $z \approx 4$.

Aletheia (Ἀλήθεια), in ancient Greek, means truth or unconcealment. In mythology, she was the personification of Truth.

Emulated Parameters

The current release of Aletheia is trained on the following key parameters (for more details, see the full documentation):

Parameter	Description
$\omega_b$	Physical baryon density parameter
$\omega_c$	Physical cold dark matter density parameter
$n_s$	Primordial scalar spectral index
$\sigma_{12}$	RMS of matter fluctuations at $R=12,{\rm Mpc}$

The emulator is trained on shape parameters spanning $\pm 5\sigma$ of Planck 2018 constraints and a wide clustering range of $0.2 < \sigma_{12} < 1.0$.

It also robustly handles variations in dark energy through the evolution mapping technique, allowing for inputs of $A_{\rm{s}}$, $w_0$, $w_a$, $\omega_{\rm DE}$ and $\omega_k$.

Getting Started

You can install the latest stable release of the code directly from PyPI:

pip install AletheiaCosmo

Once installed, you can follow the Jupyter Notebook tutorial or the Quick Start Guide for an example of how to make predictions.

A minimal example is as simple as:

import numpy as np
from aletheiacosmo import AletheiaEmu

# 1. Define cosmology using the built-in helper
cosmo_params = AletheiaEmu.create_cosmo_dict(
    h=0.67,
    omega_b=0.0224,
    omega_c=0.120,
    n_s=0.96,
    A_s=2.1e-9,
    model='LCDM'
)

# 2. Initialize the emulator
emu = AletheiaEmu()

# 3. Get the non-linear P(k) at z=1.0
# Scales to be considered, in 1/Mpc
k = np.logspace(-2, 0.3, 100)
z = 1.0
# Return the non-linear power spectrum in units of Mpc^3
p_nonlinear = emu.get_pnl(k, cosmo_params, z)

Developer Version

If you wish to modify the code or contribute to development, you can install the developer version:

# Clone the repository
git clone [https://gitlab.mpcdf.mpg.de/arielsan/aletheia.git](https://gitlab.mpcdf.mpg.de/arielsan/aletheia.git)
cd aletheia

# Install in editable mode
pip install -e .

License

This package is made publicly available under the MIT License.

Project Status

Aletheia is under active development. Follow the public repository at https://gitlab.mpcdf.mpg.de/arielsan/aletheia to ensure you are always up-to-date with the latest release.