Sequential Line Search

A C++ library for performing the sequential line search method (which is a human-in-the-loop variant of Bayesian optimization).

The core algorithm is implemented in include/sequential-line-search/*.hpp and src/*.cpp. This repository also contains the following example demos:

• bayesian_optimization_1d: A simple demo of the standard Bayesian optimization applied to a one-dimensional test function.
• sequential_line_search_nd: A simple demo of the sequential line search method applied to a multi-dimensional test function.
• bayesian_optimization_1d_gui: A visual demo of the standard Bayesian optimization applied to a one-dimensional test function.
• bayesian_optimization_2d_gui: A visual demo of the standard Bayesian optimization applied to a two-dimensional test function.
• preferential_bayesian_optimization_1d_gui: A visual demo of the preferential Bayesian optimization with a simple pairwise comparison query style applied to a one-dimensional test function.
• sequential_line_search_2d_gui: A visual interactive demo of the sequential line search method applied to a two-dimensional test function.
• sequential_line_search_photo: A visual interactive demo of the sequential line search method where a photograph is enhanced using six-dimensional parameters.

This library has a python binding, named pySequentialLineSearch.

Project Web Site

https://koyama.xyz/project/sequential_line_search/

Publication

Yuki Koyama, Issei Sato, Daisuke Sakamoto, and Takeo Igarashi. 2017. Sequential Line Search for Efficient Visual Design Optimization by Crowds. ACM Trans. Graph. 36, 4, pp.48:1--48:11 (2017). (a.k.a. Proceedings of SIGGRAPH 2017) DOI: https://doi.org/10.1145/3072959.3073598

Dependencies

Required for Core Algorithms

• Eigen http://eigen.tuxfamily.org/ (brew install eigen / sudo apt install libeigen3-dev)
• NLopt https://nlopt.readthedocs.io/ (included via gitsubmodule)
• timer https://github.com/yuki-koyama/timer (included via gitsubmodule)
• mathtoolbox https://github.com/yuki-koyama/mathtoolbox (included via gitsubmodule)
• nlopt-util https://github.com/yuki-koyama/nlopt-util (included via gitsubmodule)
• parallel-util https://github.com/yuki-koyama/parallel-util (included via gitsubmodule)

Required for Command Line Demos

• (None)

To build these demos, the CMake variable: SEQUENTIAL_LINE_SEARCH_BUILD_COMMAND_DEMOS should be set ON.

Required for Visual Demos

• Qt5 http://doc.qt.io/qt-5/ (brew install qt@5 / sudo apt install qt5-default)
• rand-util https://github.com/yuki-koyama/rand-util (included via gitsubmodule)
• tinycolormap https://github.com/yuki-koyama/tinycolormap (included via gitsubmodule)

To build these demos, the CMake variable: SEQUENTIAL_LINE_SEARCH_BUILD_VISUAL_DEMOS should be set ON.

Required for Photo Enhancement Demos

• Qt5 http://doc.qt.io/qt-5/ (brew install qt@5 / sudo apt install qt5-default)
• enhancer https://github.com/yuki-koyama/enhancer (included via gitsubmodule)
• tinycolormap https://github.com/yuki-koyama/tinycolormap (included via gitsubmodule)

To build these demos, the CMake variable: SEQUENTIAL_LINE_SEARCH_BUILD_PHOTO_DEMOS should be set ON. They require runtime environments to support OpenGL 3.2 Core Profile and GLSL 3.3.

Required for Experimental Python Binding

• pybind11 https://github.com/pybind/pybind11 (included via gitsubmodule)

To enable python binding, the CMake variable: SEQUENTIAL_LINE_SEARCH_BUILD_PYTHON_BINDING should be set ON.

How to Compile and Run (C++)

We use cmake (3.3 or above) for managing the source codes. You can compile the core module and the demo applications at once by, for example,

git clone https://github.com/yuki-koyama/sequential-line-search.git --recursive
cd sequential-line-search
mkdir build
cd build
cmake ../
make

Then you can run the applications by, for example,

./demos/sequential_line_search_nd/SequentialLineSearchNd

We tested on macOS (10.15) only. We are aware that the visual demos cannot be built as it is in other OSs; some OpenGL paths etc. need to be resolved. Pull requests welcome.

How to Install (Python)

pySequentialLineSearch is a subset of Python bindings of the C++ library. Tested on Python 3.6, 3.7, and 3.8.

It can be installed via PyPI:

pip install git+https://github.com/yuki-koyama/sequential-line-search

Prerequisites

macOS

brew install cmake eigen

Ubuntu 18.04/20.04

sudo apt install cmake libeigen3-dev

Examples

Note: User interaction part is omitted from these examples.

C++

#include <iostream>
#include <sequential-line-search/sequential-line-search.hpp>

using Eigen::VectorXd;
using sequential_line_search::SequentialLineSearchOptimizer;

double AskHumanForSliderManipulation(const std::pair<VectorXd, VectorXd>& slider_ends)
{
    // ...
    // ...

    return slider_position;
}

int main()
{
    // Instantiate an optimizer
    constexpr int dim = 6;
    SequentialLineSearchOptimizer optimizer(dim);

    // Iterate optimization steps
    constexpr int num_iters = 15;
    for (int i = 0; i < num_iters; ++i)
    {
        // Retrieve a slider space
        const std::pair<VectorXd, VectorXd> slider_ends = optimizer.GetSliderEnds();

        // Query slider manipulation
        const double slider_position = AskHumanForSliderManipulation(slider_ends);

        // Feed the slider manipulation result to the optimizer
        optimizer.SubmitLineSearchResult(slider_position);
    }

    // Display the found solution
    std::cout << optimizer.GetMaximizer() << std::endl;

    return 0;
}

Python

import pySequentialLineSearch
import numpy

def ask_human_for_slider_manipulation(slider_ends):
    # ...
    # ...

    return slider_position

def main():
    optimizer = pySequentialLineSearch.SequentialLineSearchOptimizer(6)

    for i in range(15):
        slider_ends = optimizer.get_slider_ends()
        slider_position = ask_human_for_slider_manipulation(slider_ends)
        optimizer.submit_line_search_result(slider_position)

    print(optimizer.get_maximizer())

if __name__ == '__main__':
    main()

Supported Environments

We have tested the C++ portion of our codebase on macOS using the clang compiler and on Ubuntu 20.04 using the g++ compiler. As for the Python portion, it has been tested on versions 3.7 through 3.11.

Technical Details

Gaussian Process Kernel

• ARD Matern 5/2 kernel (default; recommended in [Snoek et al. NIPS 2011])
• ARD squared exponential kernel (used in [Koyama et al. SIGGRAPH 2017])

Gaussian Process Kernel Hyperparameters

The optimizer API takes a boolean named use_map_hyperparameters as input. If this is true, the optimizer calculates the kernel hyperparameters for every iteration via the MAP estimation, as described in [Koyama et al. SIGGRAPH 2017]. If this is false, the optimizer just uses default values, making the optimization more efficient.

Finding Maximizer of Acquisition Function

Finding the global maximizer of the acquisition function is a difficult problem since it often has multiple local maxima and is high-dimensional.

This implementation offers two approaches for this problem:

• The first option is to perform DIRECT (a derivative-free global optimization algorithm) and then refine the solution using L-BFGS (a gradient-based local optimization algorithm).
• The second option is to perform L-BFGS multiple times with many different initial solutions and then pick up the best solution.

See src/acquisition-function.cpp for details.

Acquisition Function Choices

The following acquisition functions are supported:

• Expected improvement (EI) [default; used in the original paper]
• Gaussian process upper confidence bound (GP-UCB)

Search Space

This implementation assumes that the search space is always [0, 1]^D. When you want to handle a different search space, you need to normalize the target space into [0, 1]^D manually.

Construction of Slider Space

A slider space is constructed by choosing two end points. One of the two end points is always selected by maximizing the acquisition function (i.e., x^{EI} when using EI as the acquisition function). The other end point is selected by one of the following options:

• The point that provides the largest expected value (i.e., x^{+}) (default; used in the original paper)
• The point that is selected in the last subtask (i.e., x^{chosen}) (suggested in [Koyama+, 2020])

See Also

Sequential Gallery (SIGGRAPH 2020) is a more recent publication on the same topic (i.e., human-in-the-loop design optimization).

• Project page: https://koyama.xyz/project/sequential_gallery/
• GitHub: https://github.com/yuki-koyama/sequential-gallery

BO as Assistant (UIST 2022) is a research project using this library for a different purpose (i.e., for generating design suggestions during slider manipulation).

• Project page: https://koyama.xyz/project/bo-as-assistant/

License

MIT License.

Contributing

Issue reports, suggestions, requests, and PRs are highly welcomed.

Contact

Yuki Koyama ([email protected])