Introduction

libROM is a library to compute proper orthogonal decomposition-based reduced order models (POD-based ROMs). It also contains some code to compute hyperreduced POD-based ROMs using the discrete empirical interpolation method (DEIM).

Authors

The original libROM release was written by Bill Arrighi based on prototype MATLAB code written by Geoffrey Oxberry and Kyle Chand. This MATLAB code implemented the algorithm presented in

Geoffrey M. Oxberry, Tanya Kostova-Vassilevska, William Arrighi, and Kyle Chand, Limited-memory adaptive snapshot selection for proper orthogonal decomposition, International Journal of Numerical Methods in Engineering, 109:198--217.

The key algorithmic idea of computing an SVD incrementally to train POD-based ROMs on the fly was conceived by Kyle Chand and refined by Geoffrey Oxberry based on his PhD thesis work, with collaborative contributions by Bill Arrighi and Tanya Kostova-Vassilevska.

Subsequent commits to libROM have been made by Geoffrey Oxberry, Robert W. Anderson, Youngsoo Choi, and Dylan Copeland. In particular, Bill Arrighi and Robert W. Anderson have contributed an implementation of DEIM to libROM, and Dylan Copeland has contributed an implementation of GNAT to libROM.

License

libROM is distributed under the terms of both the MIT license and the Apache License (Version 2.0). Users may choose either license at their option.

All new contributions must be made under both the MIT and Apache-2.0 licenses.

See LICENSE-MIT, LICENSE-APACHE, COPYRIGHT, and NOTICE for details.

Up to commit 299876e0a0304f25db56f1f9e2eb2c61ef199048, libROM was previously released under the terms of the BSD-3 license.

SPDX_License-Identifier: (Apache-2.0 OR MIT)

LLNL-CODE-686965 (up to commit 299876e0a0304f25db56f1f9e2eb2c61ef199048) LLNL-CODE-766763

Installation

See the INSTALL file for details; in brief, it uses the configure, make, make install sequence of commands, but you probably want to check out the INSTALL file for some guidance on flags, or the output of ./configure --help.

For developers who need to hack the build system

If you want to add new source files and executables, the best way to do so is to modify Makefile.am, which is a GNU Automake file.

If you want to add new dependencies (e.g., you want to use a new linear algebra library), the best way to add all of the include/link flag information is to modify configure.ac, which is a GNU Autoconf file. As part of modifying this file, if you want to add new macros copied from an m4sh macro library, add them to the config folder.

After changing configure.ac or Makefile.am, run the following command in the root of this repository:

autoreconf -I config --install

A full explanation of GNU Autotools is out of the scope of this README, but briefly:

• aclocal takes configure.ac and a bunch of m4sh files -- these all have the suffix .m4 and makes an aclocal.m4 file containing all of the macros needed by configure.ac

• autoconf takes configure.ac and aclocal.m4 and generates a configure script

• automake takes Makefile.am, configure.ac, and aclocal.m4 and generates a Makefile.in file

• configure takes Makefile.in and generates a Makefile, which can be used with GNU Make to build and install libROM

The autoreconf command runs these tools -- and others -- in the correct order to generate a working configure script, along with all of the necessary intermediate files, some of which were mentioned in the previous list.

The following resources are moderately useful at communicating how to modify these files, in (roughly) descending order of utility:

• Wikipedia article on GNU Autotools: Start here. Mostly useful for the diagram explaining the inputs and outputs of each tool, plus their dependency relationships

• Autotools Mythbuster: Read after the Wikipedia article. Good at communicating the basics, but occasionally misses important finer points (e.g., how to add include flags and link flags to Automake files).

• GNU Automake Manual: Ignore all of Chapter 1 and Chapter 2, except Section 2.4. Section 2.4 illustrates the basics covered in Autotools Mythbuster, but more verbosely. If you're in a hurry and you're getting errors due to configure.ac, skip to Section 6.1. If you're in a hurry and you want to figure out how to hack Makefile.am, skip to Chapter 8 if you're trying to add source files or executables. Skip to Chapter 9 if you're trying to add commands to call scripts, generate headers, generate example data, etc. Skip to Chapter 15 if you're trying to add test harnesses.

• GNU Autoconf Manual: Autotools Mythbuster has a better introduction; use this resource if you get stuck.

• GNU Autoconf Archive: Collection of prebuilt m4sh macros for autoconf. Useful to search for macros that might do what you need (e.g., detect C++ features). To "install" a macro from here, add a text file with the macro to the config directory.

• GNU Manuals: Useful if you get really stuck, and the problem is in some other part of the GNU Autotools, but try searching for your problem on Google first.

• Autotools Tutorial: Lengthy introduction at a much slower pace than Autotools Mythbuster or the GNU Autotools manuals. The format is 500+ LaTeX Beamer slides as a big PDF, and is more suitable for a half-day to day-long workshop. You're likely to find what you want to know faster by searching/reading the previous resources.