Keplearn Launches Rust Symbolic Regression Engine for Instant Equation Extraction

Keplearn

Symbolic regression in seconds.

Keplearn is named after Johannes Kepler, who deduced his laws of planetary motion by studying tables of astronomical observations taken by Tycho Brahe. That is what this program attempts to do: given columns of measurements, find the compact law that relates them.

    m1   |  m2   |  r   | force
   ------+-------+------+-------
    1.0  |  2.0  | 1.0  |  2.00
    2.0  |  2.0  | 2.0  |  1.00        ┌──────────┐
    1.5  |  3.0  | 3.0  |  0.50  ──►   │ keplearn │ ──►   force = m1 * m2 / r**2
    2.5  |  1.0  | 0.5  | 10.00        └──────────┘
    3.0  |  4.0  | 2.0  |  3.00

More formally, it's a deterministic symbolic regression engine (written in Rust) that recovers closed-form equations from tabular data by best-first recursive reduction.

• Reads a TSV or CSV from stdin, prints candidate equations as JSON
• Single binary, zero dependencies (fully static with the musl target)
• Designed to answer in seconds: exact laws usually resolve in milliseconds, and --timeout caps the hard cases
• Deterministic; the same input produces the same output, byte for byte
• The reported r2 is computed from the printed equation itself, never from an internal fitting stage
• Fitted constants snap to rationals and multiples of pi, e, and sqrt(2), with every snap verified before it is kept

Download

macOS (universal: Apple Silicon and Intel)

curl -L -o keplearn https://github.com/owls-on-wires/keplearn/releases/latest/download/keplearn-macos-universal
chmod +x keplearn
./keplearn --help

Windows (PowerShell)

curl.exe -L -o keplearn.exe https://github.com/owls-on-wires/keplearn/releases/latest/download/keplearn-windows-x86_64.exe
.\keplearn.exe --help

Linux (x86_64, fully static)

curl -L -o keplearn https://github.com/owls-on-wires/keplearn/releases/latest/download/keplearn-linux-x86_64
chmod +x keplearn
./keplearn --help

Usage

Name the column to predict with --target (the default is a column called target) and pipe in a TSV or CSV with a header row. The delimiter comes from the header: tab if present, else comma.

$ ./keplearn --target force --top-k 1 --pretty --out laws.json < gravity.tsv
$ cat laws.json
{
  "results": [
    {
      "expr": "((x1**(1))*(x2**(1))*(x3**(-2)))",
      "r2": 1.0000000000,
      "search_r2": 1.0000000000,
      "holdout_r2": 0.9999999999998754,
      "scale": 0.9999984680738088,
      "offset": 0.000011830325937959667,
      "columns": [
        0,
        1,
        2
      ],
      "factor": "direct",
      "model": "((x1*x2)*((x3)**(-2)))"
    }
  ],
  "time_ms": 0,
  "n_expressions": 0,
  "n_evaluated": 0,
  "stopped_by": "exact_exit"
}

x1..xN are the feature columns in file order, target excluded; here x1=m1, x2=m2, x3=r, so the recovered law reads m1*m2/r**2. Candidates arrive best-first: results[0].model is the answer and its r2 is scored on the supplied data. Diagnostics print to stderr, so stdout is always one JSON object.

Useful flags:

./keplearn --target Tc --timeout 60000 < superconductors.csv   # cap the search at 60 s
./keplearn --top-k 3 < data.tsv                                # emit the 3 best candidates
./keplearn --target y --sample 1000 < big.tsv                  # screen on more rows
./keplearn --help                                              # full flag list and output schema

Method

The engine searches over chains of invertible reductions applied to the target column: it divides out a fitted factor, inverts a transform such as log, sqrt, or arcsin, fits an inner affine node, and repeats this to a fixed depth. At each node it attempts a terminal fit of the reduced target with an affine monomial whose exponents come from a log-linear regression, with a sparse k-term monomial, or with one of a small set of composite forms (L2 norms, rationals, trig). Candidates are ranked on an internal 25% holdout with an MDL complexity penalty.

Fitted constants are snapped to nearby rationals and to multiples of pi, e, and sqrt(2). A snap is kept only when a verification pass shows the model still scores as well on holdout and full data. The winning expression is then simplified algebraically, refit for scale and offset against the full dataset, and re-scored. The r2 in the output comes from evaluating the printed model string; it is not carried over from any internal fitting stage.

Benchmarks

Keplearn is a method in SRBench, the standard symbolic regression benchmark, added in cavalab/srbench#223.

These numbers come from SRBench's own containerized pipeline, graded by its sympy equivalence check, at one trial per dataset and a 60 second per-fit budget. Ground-truth symbolic solution rate by target noise:

The highest published Feynman symbolic rate on SRBench is AIFeynman at 55.8%, with the next group near 27%; Keplearn reaches 64.7% at a fraction of their compute budget.

On the 138 black-box datasets, which have no closed-form ground truth, the median test R2 is near zero (about -0.003). Keplearn targets exact analytic laws rather than general curve fitting, and that result reflects the trade-off.

Fit time under the same 60 second cap, one core per fit:

Solved cases exit early. At noise 0, half the Feynman suite finishes in under a second; under noise the exact-exit path cannot fire, so those fits run to the cap.