# exojax | Hajime Kawahara | Knowledge Base | Instagit

🐈 Differentiable Spectrum Modeling of Exoplanets and Brown Dwarfs

GitHub Stars: 67

Repository: https://github.com/hajimekawahara/exojax

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## Articles

### [How to Define Custom Molecular Opacities or Add New Species to ExoJAX](/hajimekawahara/exojax/how-can-i-define-custom-molecular-opacities-or-add-new-species-to-exojax)

Learn how to define custom molecular opacities and add new species to ExoJAX. Follow our guide to enhance your exoplanet atmosphere modeling capabilities.

- Tags: how-to-guide
- Published: 2026-03-03

### [How ExoJAX Supports HMC-NUTS and SVI for Bayesian Atmospheric Retrieval](/hajimekawahara/exojax/how-does-exojax-support-advanced-inference-techniques-like-hmc-nuts-and-svi)

ExoJAX enables advanced Bayesian atmospheric retrieval with HMC-NUTS and SVI. Leverage its JAX-based pipeline with NumPyro and Blackjax for efficient MCMC sampling and variational inference on exoplanet spectra.

- Tags: deep-dive
- Published: 2026-03-03

### [The Role of JAX in ExoJAX: Performance and Scalability for Exoplanet Modeling](/hajimekawahara/exojax/what-is-the-role-of-jax-in-exojaxs-performance-and-scalability-for-exoplanet-modeling)

Discover how JAX powers ExoJAX for high performance and scalability in exoplanet modeling. Accelerate your simulations with JIT compilation and automatic differentiation.

- Tags: performance
- Published: 2026-03-03

### [How to Perform Reflection Spectrum Calculations Using ExoJAX](/hajimekawahara/exojax/how-can-i-perform-reflection-spectrum-calculations-using-exojax)

Learn to perform reflection spectrum calculations with ExoJAX. This guide explores its JAX pipeline and radiative transfer solvers for efficient, differentiable atmospheric retrieval.

- Tags: how-to-guide
- Published: 2026-03-03

### [Data Formats Compatible with ExoJAX's Database and Data Modules: A Complete Guide](/hajimekawahara/exojax/what-data-formats-are-compatible-with-exojaxs-database-and-data-modules)

Explore data formats ExoJAX supports including ExoMol HITRAN VALD and more. Our guide details native spectroscopic formats compatible with ExoJAX modules.

- Tags: how-to-guide
- Published: 2026-03-03

### [How to Apply Instrumental Broadening Effects to Simulated Spectra in ExoJAX](/hajimekawahara/exojax/how-do-i-apply-instrumental-broadening-effects-to-my-simulated-spectra-in-exojax)

Learn how to apply instrumental broadening effects to simulated spectra in ExoJAX. Convert resolution to Gaussian std, instantiate SopInstProfile, and convolve your spectrum with ipgauss.

- Tags: how-to-guide
- Published: 2026-03-03

### [How to Set Up Temperature-Pressure Profiles in ExoJAX: Complete Configuration Guide](/hajimekawahara/exojax/what-are-the-requirements-for-setting-up-temperature-pressure-profiles-in-exojax)

Learn to set up temperature pressure profiles in ExoJAX. Configure analytic functions or custom arrays with this complete guide for accurate atmospheric modeling.

- Tags: how-to-guide
- Published: 2026-03-03

### [How ExoJAX Integrates Spectral Lines and Continua: A Deep Dive into the Opacity Pipeline](/hajimekawahara/exojax/how-does-exojax-handle-the-integration-of-spectral-lines-and-continua)

ExoJAX integrates spectral lines and continua by calculating separate cross-sections and absorption coefficients converting them to layer optical depth matrices and summing into a total dtau matrix for radiative transfer.

- Tags: deep-dive
- Published: 2026-03-03

### [How to Configure ExoJAX to Use Different Opacity Calculation Methods (Premodit vs Modit)](/hajimekawahara/exojax/how-can-i-configure-exojax-to-use-different-opacity-calculation-methods-like-premodit-or-modit)

Learn how to configure ExoJAX for different opacity calculation methods. Easily switch between Premodit and Modit for your atmospheric modeling needs with this guide.

- Tags: how-to-guide
- Published: 2026-03-03

### [How ExoJAX's Atmospheric Microphysics (AMP) Class Models Cloud Properties](/hajimekawahara/exojax/how-does-exojaxs-atmospheric-microphysics-amp-class-model-cloud-properties)

Learn how ExoJAX's AmpAmcloud class models cloud properties using the Ackerman & Marley (2001) framework. Understand particle size distributions and mixing ratios.

- Tags: internals
- Published: 2026-03-03

### [ExoJAX Spectral Operator (Sop) Class: Rotation, Instrumental Broadening, and Photometry](/hajimekawahara/exojax/what-functionalities-does-the-spectral-operator-sop-class-provide-for-exojax-such-as-rotation-and-instrumental-broadening)

Explore the ExoJAX Spectral Operator (Sop) class for unified spectral processing including rotation, instrumental broadening, and photometry. Learn how to apply these effects efficiently using FFT or Overlap-and-Add.

- Tags: deep-dive
- Published: 2026-03-03

### [How to Use ArtEmis, ArtTrans, and ArtReflect Classes for Radiative Transfer in ExoJAX](/hajimekawahara/exojax/how-do-i-use-the-artemis-arttrans-and-artreflect-classes-for-radiative-transfer-in-exojax)

Master radiative transfer in ExoJAX! Learn to use ArtEmis, ArtTrans, and ArtReflect classes for emission, transmission, and reflection spectra with JAX-accelerated kernels. Get accurate exoplanet atmospheric data.

- Tags: how-to-guide
- Published: 2026-03-03

### [How ExoJAX Opacity Calculators Handle Voigt Profiles, CIA, Mie, and Rayleigh Scattering](/hajimekawahara/exojax/how-do-exojaxs-opacity-calculators-opa-handle-voigt-profiles-cia-mie-and-rayleigh-scattering)

Explore how ExoJAX opacity calculators leverage a modular framework for Voigt profiles, CIA, Rayleigh, and Mie scattering. Achieve differentiable, GPU-accelerated radiative transfer.

- Tags: tutorial
- Published: 2026-03-03

### [ExoJAX Molecular, Atomic, and Continuum Database Classes: Key Differences Explained](/hajimekawahara/exojax/what-are-the-key-differences-between-exojaxs-molecular-mdb-atomic-adb-and-continuum-cdb-database-classes)

Understand ExoJAX's molecular, atomic, and continuum database classes: MdbExomol, AdbVald, and CdbCIA. Learn their data formats, caching, and GPU workflows for radiative transfer.

- Tags: deep-dive
- Published: 2026-03-03

### [How ExoJAX Enables Gradient-Based Optimization for Atmospheric Retrieval](/hajimekawahara/exojax/how-does-exojax-support-gradient-based-optimization-for-atmospheric-retrieval)

Discover how ExoJAX enables gradient-based optimization for atmospheric retrieval by making the full forward model differentiable with JAX. Get exact gradients without manual coding.

- Tags: internals
- Published: 2026-03-03

### [How to Access and Utilize Built-in Data Files and Test Data within ExoJAX](/hajimekawahara/exojax/how-do-i-access-and-utilize-built-in-data-files-and-test-data-within-exojax)

Access ExoJAX built-in data files and test data reliably use get_testdata_filename() for absolute paths. Learn how to utilize these assets easily.

- Tags: how-to-guide
- Published: 2026-03-03

### [ExoJAX Plotting Capabilities: A Complete Guide to Visualizing Spectral Data and Model Outputs](/hajimekawahara/exojax/what-plotting-capabilities-does-exojax-offer-for-visualizing-spectral-data-and-model-outputs)

Explore ExoJAX plotting capabilities for visualizing spectral data and model outputs. This guide covers radiative transfer, opacity grids, matrices, and contribution functions using exojax.plot.

- Tags: tutorial
- Published: 2026-03-03

### [ExoJAX Utility Functions for Spectral Modeling: A Complete Guide](/hajimekawahara/exojax/what-utility-functions-are-available-in-exojax-for-common-spectral-modeling-tasks)

Explore ExoJAX utility functions for spectral modeling. Discover helpers for grids, photometry, opacity, and data validation in radiative transfer.

- Tags: how-to-guide
- Published: 2026-03-03

### [ExoJAX Atmospheric Models: Temperature-Pressure Profiles and Cloud Microphysics Guide](/hajimekawahara/exojax/where-can-i-find-information-on-exojaxs-atmospheric-models-including-temperature-pressure-profiles-and-cloud-microphysics)

Explore ExoJAX's comprehensive atmospheric models. Find resources for temperature-pressure profiles and Ackerman-Marley cloud microphysics. Learn more at hajimekawahara/exojax.

- Tags: guide
- Published: 2026-03-03

### [How ExoJAX Implements Radiative Transfer Calculations for Emission and Transmission Spectra](/hajimekawahara/exojax/how-does-exojax-implement-radiative-transfer-calculations-for-emission-and-transmission-spectra)

ExoJAX uses a JAX-first engine for fast radiative transfer calculations. Explore its JIT-compiled solvers for emission and transmission spectra on GPUs and TPUs.

- Tags: how-to-guide
- Published: 2026-03-03

### [How to Select and Use Molecular and Atomic Databases (ExoMol, HITRAN, VALD) in ExoJAX](/hajimekawahara/exojax/how-do-i-select-and-use-molecular-and-atomic-databases-exomol-hitran-vald-in-exojax)

Learn how to select and use molecular and atomic databases like ExoMol HITRAN and VALD in ExoJAX. Efficiently integrate spectroscopic line lists for advanced radiative transfer calculations.

- Tags: how-to-guide
- Published: 2026-03-03

### [ExoJAX Opacity Calculation Methods: Premodit, Modit, LPF, and CKD Explained](/hajimekawahara/exojax/what-are-the-different-opacity-calculation-methods-supported-by-exojax-premodit-modit-lpf-ckd)

Explore ExoJAX opacity calculation methods: Premodit Modit LPF and CKD. Discover JAX compatible classes for balancing speed and accuracy in spectral analysis.

- Tags: deep-dive
- Published: 2026-03-03

### [How ExoJAX Leverages JAX for Automatic Differentiation in Spectral Modeling](/hajimekawahara/exojax/how-does-exojax-leverage-jax-for-automatic-differentiation-in-spectral-modeling)

Explore how ExoJAX uses JAX transformations like grad, jit, and vmap for automatic differentiation in spectral modeling. Optimize radiative transfer models with exact derivatives.

- Tags: deep-dive
- Published: 2026-03-03