nlsq 0.4.1

GPU/TPU accelerated nonlinear least-squares curve fitting using JAX

NLSQ: GPU-Accelerated Curve Fitting

Drop-in replacement for scipy.optimize.curve_fit with 150-270x speedup on GPU

Documentation | Examples | API Reference | ArXiv Paper

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What is NLSQ?

NLSQ is a nonlinear least squares curve fitting library built on JAX. It provides:

• SciPy-compatible API - Same function signatures as scipy.optimize.curve_fit
• GPU/TPU acceleration - JIT-compiled kernels via XLA
• Automatic differentiation - No manual Jacobian calculations needed
• Large dataset support - Handles 100M+ data points with streaming optimization

Installation

# CPU (all platforms)
pip install nlsq

# GPU (Linux with CUDA 12.1+)
pip install nlsq
pip install "jax[cuda12-local]==0.8.0"

Verify GPU installation

python -c "import jax; print('Devices:', jax.devices())"
# Expected: [cuda(id=0)] for GPU, [CpuDevice(id=0)] for CPU

Quick Start

import numpy as np
import jax.numpy as jnp
from nlsq import curve_fit


# Define model function (use jax.numpy for GPU acceleration)
def exponential(x, a, b, c):
    return a * jnp.exp(-b * x) + c


# Generate data
x = np.linspace(0, 4, 1000)
y = 2.5 * np.exp(-0.5 * x) + 1.0 + 0.1 * np.random.randn(len(x))

# Fit - same API as scipy.optimize.curve_fit
popt, pcov = curve_fit(exponential, x, y, p0=[2.0, 0.5, 1.0])

print(f"Parameters: a={popt[0]:.3f}, b={popt[1]:.3f}, c={popt[2]:.3f}")
print(f"Uncertainties: {np.sqrt(np.diag(pcov))}")

Key Features

Feature	Description
Automatic Jacobians	JAX's autodiff eliminates manual derivatives
Bounded optimization	Trust Region Reflective and Levenberg-Marquardt
Large datasets	Chunked and streaming optimizers for 100M+ points
Multi-start	Global optimization with LHS/Sobol sampling
Mixed precision	Automatic float32→float64 upgrade when needed
Workflow system	Auto-selects strategy based on dataset size
CLI interface	YAML-based workflows with nlsq fit and nlsq batch

Performance

NLSQ shows increasing speedups as dataset size grows:

Dataset Size	SciPy (CPU)	NLSQ (GPU)	Speedup
10K points	15ms	2ms	7x
100K points	150ms	3ms	50x
1M points	1.5s	8ms	190x
10M points	15s	55ms	270x

Note: First call includes JIT compilation (~500ms). Subsequent calls reuse compiled kernels.

See Performance Guide for benchmarks.

Large Dataset Example

from nlsq import fit
import numpy as np
import jax.numpy as jnp


def model(x, a, b, c):
    return a * jnp.exp(-b * x) + c


# 50 million points
x = np.linspace(0, 10, 50_000_000)
y = 2.0 * np.exp(-0.5 * x) + 0.3 + np.random.normal(0, 0.05, len(x))

# Auto-selects optimal strategy (chunked/streaming) based on memory
popt, pcov = fit(model, x, y, p0=[2.5, 0.6, 0.2], show_progress=True)

Advanced Usage

Multi-start global optimization

from nlsq import curve_fit

popt, pcov = curve_fit(
    model,
    x,
    y,
    p0=[1, 1, 1],
    bounds=([0, 0, 0], [10, 5, 10]),
    multistart=True,
    n_starts=20,
    sampler="lhs",
)

Workflow presets

from nlsq import fit

# Presets: 'fast', 'robust', 'global', 'quality', 'memory_efficient'
popt, pcov = fit(model, x, y, preset="robust")

Numerical stability

from nlsq import curve_fit

# Auto-detect and fix numerical issues
popt, pcov = curve_fit(model, x, y, p0=p0, stability="auto")

Memory management

from nlsq import MemoryConfig, memory_context, CurveFit

config = MemoryConfig(memory_limit_gb=8.0, enable_mixed_precision_fallback=True)

with memory_context(config):
    cf = CurveFit()
    popt, pcov = cf.curve_fit(model, x, y, p0=p0)

Command-line interface

# Single workflow
nlsq fit experiment.yaml

# Batch processing
nlsq batch configs/*.yaml --summary results.json

# System info
nlsq info

See CLI Reference for YAML configuration.

See Advanced Features for complete documentation.

Examples

Start with the Interactive Tutorial on Google Colab.

By topic:

• Getting Started - Basic usage and quickstart
• Core Tutorials - Large datasets, bounded optimization
• Advanced - GPU optimization, streaming, checkpointing
• Applications - Physics, chemistry, biology, engineering

See examples/README.md for the full index.

Requirements

• Python 3.12+
• JAX 0.8.0 (locked version)
• NumPy 2.0+
• SciPy 1.14.0+

GPU support (Linux only): CUDA 12.1-12.9, NVIDIA driver >= 525

Citation

If you use NLSQ in your research, please cite:

@software{nlsq2024,
  title={NLSQ: Nonlinear Least Squares Curve Fitting for GPU/TPU},
  author={Chen, Wei and Hofer, Lucas R and Krstaji{\'c}, Milan and Smith, Robert P},
  year={2024},
  url={https://github.com/imewei/NLSQ}
}

@article{jaxfit2022,
  title={JAXFit: Trust Region Method for Nonlinear Least-Squares Curve Fitting on the {GPU}},
  author={Hofer, Lucas R and Krstaji{\'c}, Milan and Smith, Robert P},
  journal={arXiv preprint arXiv:2208.12187},
  year={2022}
}

Acknowledgments

NLSQ is an enhanced fork of JAXFit by Lucas R. Hofer, Milan Krstajić, and Robert P. Smith. We gratefully acknowledge their foundational work.

License

MIT License - see LICENSE for details.