Getting Started

Installation

We recommend using a fresh virtual environment via tools like conda or uv with Python 3.11+:

uv venv mythos --python 3.11
source mythos/bin/activate

conda create -y -n mythos python=3.11
conda activate mythos

Depending on your hardware, you may want to install the GPU-accelerated version of JAX. See the JAX installation docs for details. If you don’t need GPU support, you can skip straight to installing mythos (which installs the CPU version of JAX automatically).

Install mythos using pip:

pip install mythos-bio

Note

The PyPI package name is mythos-bio, but it installs as mythos (use import mythos in your code).

Some simulator backends have additional dependencies:

  • oxDNA: install separately. See Simulators.

  • GROMACS: install separately, ensure gmx is on PATH. See Simulators.

  • LAMMPS: install separately with CG-DNA package. See Simulators.

Quick Overview

The two primary use cases for mythos are:

  1. Running differentiable simulations using one of several backends (JAX-MD, oxDNA, GROMACS, LAMMPS). See Simulators for the full list.

  2. Optimizing force field parameters against target observable values, which can be ``top-down’’ (experimentally derived) or ``bottom-up’’ (derived from more fine-grained models). See Optimization for the framework details.

Energy functions define the physics of the biomolecular model and typically house the parameters being optimized (though optimization with respect to other simulation parameters, such as temperature, number of particles, etc. is possible). See Energy Functions for currently available models and how to extend them or develop a bespoke model.

Observables compute measurable quantities (e.g. helical pitch, persistence length, membrane thickness, bond and angle distributions, etc.) from trajectories. Observables are packaged into objectives and fed into loss functions. See Observables for the full catalog and API.

Example: oxDNA Optimization with DiffTRe

Below is a minimal example of optimizing oxDNA energy function parameters against a propeller twist target using the DiffTRe algorithm. This demonstrates how the core pieces — simulator, energy function, observable, loss function, objective, and optimizer — fit together.

import functools
import typing
from pathlib import Path

import jax
import jax.numpy as jnp
import optax

import mythos.energy.dna1 as dna1_energy
import mythos.observables as jd_obs
import mythos.simulators.oxdna as oxdna
from mythos.input import topology
from mythos.optimization.objective import DiffTReObjective
from mythos.optimization.optimization import SimpleOptimizer

jax.config.update("jax_enable_x64", True)

# --- Simulator environment and energy function ---
input_dir = Path("data/templates/simple-helix")
top = topology.from_oxdna_file(input_dir / "sys.top")

energy_fn = dna1_energy.create_default_energy_fn(top)

simulator = oxdna.oxDNASimulator(
    input_dir=input_dir,
    energy_fn=energy_fn,
    source_path=Path("../oxDNA").resolve(),
)

# --- Observable & loss function ---
prop_twist_obs = jd_obs.propeller.PropellerTwist(
    rigid_body_transform_fn=transform_fn,
    h_bonded_base_pairs=jnp.array([
        [1, 14], [2, 13], [3, 12], [4, 11], [5, 10], [6, 9]
    ]),
)
target = 21.7 # degrees

def loss_fn(traj, weights, **_args):  # We only use traj and weights
    measured = jnp.dot(weights, prop_twist_obs(traj))
    loss = jnp.sqrt((measured - target) ** 2)
    return loss, (("prop_twist", measured), {})

# --- Objective & optimizer ---
objective = DiffTReObjective(
    name="propeller_twist",
    required_observables=simulator.exposes(),
    energy_fn=energy_fn,
    grad_or_loss_fn=loss_fn,
    n_equilibration_steps=0,
    min_n_eff_factor=0.95,
)

opt = SimpleOptimizer(
    objective=objective,
    simulator=simulator,
    optimizer=optax.adam(learning_rate=1e-3),
)
opt.run(opt_params, n_steps=100)

More Examples

The examples directory in the repository contains runnable examples for a variety of scenarios:

Simulations:

Optimizations:

Custom energy functions:

Where to Go Next