SciJIT (scijit)

📖 Documentation: https://shmuel-gilbaum.github.io/SciJit/

A scipy-equivalent library callable from inside numba @njit code. scijit either wraps the same Fortran packs scipy wraps, or re-implements scipy's pure-Python routines as @njit. Results match scipy, checked routine by routine against it during development. Where a routine differs from scipy, its Notes say so; an argument it does not implement raises rather than silently returning something else. It pays off most when the same routine runs many times inside a compiled loop, where scipy would pay Python's per-call overhead on every iteration. Same namespaces, same names, same grouping. Not every scipy subpackage is mirrored; see docs/roadmap.md for the gaps.

scijit is not affiliated with, or endorsed by, the NumPy, SciPy or Numba projects. It is also distinct from numba-scipy, which provides numba support for a small part of scipy.special.

The approach comes from NumbaMinpack (Nicholas Wogan): reach a compiled Fortran pack from @njit through a @cfunc address and a bind(c) wrapper. scijit applies it across many packs. See docs/credits.md.

scipy's classes are called like spl(x), but a numba jitclass has no __call__, so a compiled class cannot be called that way. To mirror scipy, scijit uses scijitclass, a companion package that adds __call__ to numba jitclasses, so scijit's classes keep scipy's call syntax inside @njit. It is a standalone @jitclass replacement, usable in any numba project.

Anything numba already handles is out of scope: the numpy features numba supports, and the scipy.special subset numba-scipy covers.

scijit was written mostly with Anthropic's Claude (via Claude Code) under my direction. I set the architecture and the design choices, and every routine is verified against SciPy during development.

Subpackages

Three scipy subpackages, callable from inside @njit:

• scijit.interpolate — splines and the interpolator classes (scipy.interpolate).
• scijit.optimize — roots, least squares, and minimization (scipy.optimize).
• scijit.integrate — quad, solve_ivp, odeint, and quadrature (scipy.integrate).

Each routine's coverage, backing Fortran, and scipy parity are in the usage guides and API reference. More subpackages (fft, linalg, stats, special, and others) are in development; see docs/roadmap.md.

Install

pip install scijit

The wheels bundle the compiled Fortran, so nothing extra is needed on that path. A source install compiles each Fortran pack and requires gfortran on the PATH. Full instructions and troubleshooting are in docs/install.md.

Example

Build an interpolant once, then use it inside compiled code:

import numpy as np
from numba import njit
from scijit.interpolate import CubicSpline
from scijit.integrate import simpson

# a coarse lookup table: opacity sampled at a few log-temperatures
logT   = np.array([3.0, 4.0, 5.0, 6.0, 7.0, 8.0])
logkap = np.array([0.1, 0.4, 1.2, 2.0, 1.5, 0.6])
opacity = CubicSpline(logT, logkap)        # build the interpolant once

@njit
def mean_opacity(opacity, T_lo, T_hi, n_cells=101):
    T = np.linspace(T_lo, T_hi, n_cells)
    return simpson(opacity(T), T) / (T_hi - T_lo)   # band-averaged, all in @njit

mean_opacity(opacity, 3.5, 7.5)            # -> 1.260677088

opacity(...) evaluates the spline, from Python and inside @njit, exactly as in scipy, and simpson integrates it in the same compiled function. Build the interpolant once and reuse it. A full walkthrough is in docs/getting_started.md.

Performance: when this helps

The gain comes from removing interpreter overhead, so it shows up in large or nested loops. scipy cannot be called from @njit, so it pays the interpreter on every iteration. Reproduce with python benchmarks/<name>.py:

Speedups are approximate and vary with machine, problem size and thread count. Intel SVML has been unsupported by numba since 0.62, which costs some vectorized performance on both sides of these comparisons.

The speedup tracks how much of each iteration is interpreter overhead, since that is what the compiler removes. It is not a claim about the numerics: where scijit calls Fortran, the same Fortran runs in both cases. numba also compiles on first call, which can make a single isolated call slower.

Rule of thumb:

• one large vectorized call from Python (bench_where_scipy_wins.py) → use scipy. The shipped subpackages wrap the same Fortran, so a single big call ties: a 200k-point bivariate spline evaluation matched scipy within 4%, with identical results (max|diff| 0).
• a small solve repeated many times, or nested loops → use scijit.

Documentation

The full documentation site is at https://shmuel-gilbaum.github.io/SciJit/ (Markdown sources under docs/).

• docs/getting_started.md: a first end-to-end @njit workflow.
• docs/install.md: wheel install, source install, and the import-failure note.
• docs/usage/index.md: task-by-task usage guides, one tested runnable example per function.
• docs/compatibility.md: supported versions, where agreement with scipy is bit-for-bit and where it is not, thread safety, and the prange-safety matrix.
• docs/architecture.md: what a call passes through, from the entry points down through the callback adapter, the ctypes boundary, the return types, and the jitclass rules.
• docs/roadmap.md: what is not covered yet, and why.
• docs/credits.md: provenance and the upstream library and license table.

How this project started

In 2021, during my PhD in astrophysics I was running an AGN accretion-disk simulation: a large coupled ODE system where every integration step had to solve 3 nonlinear equations at each of thousands of grid points. Both the root-solving and the variable extraction that followed depended on opacity tables, read through bivariate spline interpolation.

NumbaMinpack let me do the root-finding inside @njit code, but scipy's spline evaluators cannot be called there. So I followed NumbaMinpack's approach and wrapped the two FITPACK routines I needed for the table lookups, bispev and bispeu. The runtime dropped from unusable to a few hours.

scijit is the follow-up, built together with Claude: the whole of FITPACK instead of those two routines, then the other Fortran packs behind scipy, plus @njit versions of the routines scipy writes in Python.

License & citation

scijit wraps established numerical libraries; each subpackage carries its upstream license in src/<pack>/, and the full citation list is in CITATION.cff (GitHub "Cite this repository"). Credit details are in docs/credits.md.