Discovering physical laws with parallel symbolic enumeration

Official implementation of PSE with its core PSRN (Parallel Symbolic Regression Network) module

Authors: Kai Ruan, Yilong Xu, Ze-Feng Gao, Yike Guo, Hao Sun, Ji-Rong Wen, Yang Liu

This repository contains the official PyTorch implementation of PSE (Parallel Symbolic Enumeration): A fast and efficient symbolic expression discovery method powered by PSRN (Parallel Symbolic Regression Network). PSRN evaluates millions of symbolic expressions simultaneously on GPU with automated subtree reuse.

📥 Installation

Prerequisite: Python >=3.9, <=3.12

pip install psrn

Or build from source (https://github.com/x66ccff/PSRN):

pip install git+https://github.com/x66ccff/PSRN

🚀 Quickstart with Custom Data

Now, you can use psrn-run with custom data, use the following arguments:

Options

  -q, --csvpath TEXT           path to custom csv file

  -l, --operators         operator library (e.g., "['Add','Mul','Identity','Tanh','Abs']")
  --n_symbol_layers            number of symbol layers (default=3)
  -i, --n_inputs INTEGER       PSRN input size (n variables + n constants)
  -c, --use_constant BOOLEAN   use const in PSE

  --use_cpu BOOLEAN            use cpu
  -g, --gpu_index INTEGER      gpu index used

  --time_limit INTEGER         time limit (s)
  
  -d, --n_down_sample INTEGER  n sample to downsample in PSRN for speeding up
  -s, --seed INTEGER           seed
  -k, --topk INTEGER           number of best expressions to take from PSRN to
                               fit
  
  -o, --probe TEXT             expression probe, string, PSE will stop if
                               probe is in pf

  --experiment_name TEXT       experiment_name
  --help                       Show this message and exit.

Examples
========
>>> #   input data
>>> #  ____^______
>>> # /           |
>>> # ['x',      'y',   'x+x',        '1.5',      '3']
>>> # <-n_variables->
>>> #                 <-n_cross->
>>> #                            <-trying_const_num->
>>> # <-----------------n_inputs--------------------->

For more detailed parameter settings, please use psrn-run --help

📝 CLI Examples

Tip

• The last column of the csv should be the target variable
• If using a version of PyTorch below 2.0, an error may occur during the torch.topk operation.
• The experiments were performed on servers with Nvidia A100 (80GB) and Intel(R) Xeon(R) Platinum 8380 CPUs @ 2.30GHz.
• We recommend using a high-memory GPU as smaller cards may encounter CUDA memory errors under our experimental settings. If you experience memory issues, consider reducing the number of input slots or opting for semi_koza operator sets (e.g., replacing "Sub" and "Div" with "SemiSub" and "SemiDiv") or basic operator sets (e.g., replacing "Sub" and "Div" with "Neg" and "Inv").

To run the script with build-in custom data with an expression probe (the algorithm will stop when it finds the expression or its symbolic equivalents):

psrn-run --csvpath ./your_data.csv -g 0 -i 5 -c False --probe "(exp(x)-exp(-x))/2"

Without an expression probe:

psrn-run --csvpath ./your_data.csv -g 0 -i 5 -c False

For limited VRAM (or when the ground truth expression is expected to be simple):

psrn-run --csvpath ./your_data.csv -g 0 -i 3 -c False --probe "(exp(x)-exp(-x))/2"

To customize the operator library:

psrn-run --csvpath ./your_data.csv -g 0 -i 5 -c False --probe "(exp(x)-exp(-x))/2" -l "['Add','Mul','Identity','Tanh','Abs']"

For custom data paths and operators:

psrn-run --csvpath ./your_data.csv -g 0 -i 5 -c False -l "['Add','Mul','SemiSub','SemiDiv','Identity']" 

You can also reduce the number of layers to save VRAM (default is 3) so that you can use more inputs (e.g. 70 input PSRN, the rest 20 will be cross subtrees)

psrn-run --csvpath ./50_cols_of_x_data.csv --n_symbol_layers 2 -g 0 -i 70 -c False -l "['Add','Mul','SemiSub','SemiDiv','Identity']" 

If you want to change the source code, please use the following steps:

clone the repo first

git clone https://github.com/x66ccff/PSRN

then install the repo with edit mode

cd PSRN
pip install -e .

The cli.py is the entrance of the code, and you can change the PSRN_Regressior in regressor.py

📝 Python Examples

Show Code

import os
import click
import time
import numpy as np
import sympy as sp
import pandas as pd

default_csv = os.path.join(os.path.dirname(__file__), 'data', 'custom_data.csv')

@click.command()
@click.option("--experiment_name", default="_", type=str, help="experiment_name")
@click.option("--gpu_index", "-g", default=0, type=int, help="gpu index used")
@click.option("--operators","-l",default="['Add','Mul','Sub','Div','Identity','Sin','Cos','Exp','Log']",help="operator library")
@click.option("--n_symbol_layers",default=3,type=int,help="number of symbol layers (default=3)")
@click.option("--n_down_sample","-d",default=100,type=int,help="n sample to downsample in PSRN for speeding up")
@click.option("--n_inputs","-i",default=5,type=int,help="PSRN input size (n variables + n constants)")
@click.option("--seed", "-s", default=0, type=int, help="seed")
@click.option("--topk","-k",default=10,type=int,help="number of best expressions to take from PSRN to fit")
@click.option("--use_constant", "-c", default=False, type=bool, help="use const in PSE")
@click.option("--probe","-o",default=None,type=str,help="expression probe, string, PSE will stop if probe is in pf")
@click.option("--csvpath","-q",default=default_csv,type=str,help="path to custom csv file")
@click.option("--use_cpu",default=False,type=bool,help="use cpu")
@click.option("--time_limit", default=3600, type=int, help="time limit (s)")
def main(experiment_name, gpu_index, operators, n_down_sample, n_inputs, seed, topk, use_constant, probe, csvpath, use_cpu, time_limit):
    if not use_cpu:
        os.environ["CUDA_VISIBLE_DEVICES"] = str(gpu_index)

    import torch
    from psrn import PSRN_Regressor

    if not use_cpu:
        device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
    else:
        device = torch.device("cpu")

    operators = eval(operators)
    df = pd.read_csv(csvpath, header=None)

    Input = df.values[:, :-1].reshape(len(df), -1)
    Output = df.values[:, -1].reshape(len(df), 1)

    variables_name = [f"x{i}" for i in range(Input.shape[1])]

    regressor = PSRN_Regressor(
        variables=variables_name,
        use_const=use_constant,
        n_symbol_layers=n_symbol_layers,
        device=device,
        token_generator_config={
            "base": {
                "has_const": use_constant,
                "tokens": operators
            }
        },
        stage_config={
            "default": {
                "operators": operators,
                "time_limit": time_limit,
                "n_psrn_inputs": n_inputs,
                "n_sample_variables": 3,
            },
            "stages": [
                {},
            ],
        },
    )

    start = time.time()
    flag, pareto_ls = regressor.fit(
        Input,
        Output,
        n_down_sample=n_down_sample,
        use_threshold=False,
        threshold=1e-20,
        probe=probe,
        prun_const=True,
        prun_ndigit=6,
        top_k=topk,
    )
    end = time.time()
    time_cost = end - start

    pareto_ls = regressor.display_expr_table(sort_by='mse') # or 'reward'

    expr_str, reward, loss, complexity = pareto_ls[0]
    print('Found:', expr_str, 'time_cost', time_cost)

📚 Citation

If you use this work, please cite:

@article{ruan2025discovering,
  author     = {Ruan, Kai and Xu, Yilong and Gao, Ze-Feng and Liu, Yang and Guo, Yike and Wen, Ji-Rong and Sun, Hao},
  title      = {Discovering physical laws with parallel symbolic enumeration},
  journal    = {Nature Computational Science},
  year       = {2025},
  doi        = {10.1038/s43588-025-00904-8},
  url        = {https://www.nature.com/articles/s43588-025-00904-8}
}