Nl (format) explained

Extension:	.nl
Owner:	Robert Fourer David Gay Brian Kernighan Bell Labs
Genre:	Mathematical programming

nl is a file format for presenting and archiving mathematical programming problems.^[1] Initially, this format has been invented for connecting solvers to AMPL.^[2] It has also been adopted by other systems such as COIN-OR (as one of the input formats), FortSP (for interacting with external solvers), and Coopr (as one of its output formats).

The nl format supports a wide range of problem types, among them:

• Linear programming
• Quadratic programming
• Nonlinear programming
• Mixed-integer programming
• Mixed-integer quadratic programming with or without convex quadratic constraints
• Mixed-integer nonlinear programming
• Second-order cone programming
• Global optimization
• Semidefinite programming problems with bilinear matrix inequalities
• Complementarity problems (MPECs) in discrete or continuous variables
• Constraint programming^[3]

The nl format is low-level and is designed for compactness, not for readability. It has both binary and textual representation.Most commercial and academic solvers accept this format either directly or through special driver programs.

The open-source AMPL Solver Library distributed via Netlib^[4] and AMPL/MP library^[5] provide nl parsers that are used in many solvers.

AMPL/MP library contains an NL writer and SOL reader.

See also

• sol (format) - a file format for presenting solutions of mathematical programming problems

Notes and References

1. David Gay. Writing .nl Files. Sandia National Laboratories. 2005. Albuquerque, NM. 10.1.1.60.9659. https://web.archive.org/web/20161228202832/https://cfwebprod.sandia.gov/cfdocs/CompResearch/docs/nlwrite20051130.pdf. Dec 28, 2016. dead.
2. David Gay . Hooking Your Solver to AMPL . . 1993 . 97-4-06 . Murray Hill, NJ .
3. Robert Fourer . David M. Gay . 2002 . Extending an Algebraic Modeling Language to Support Constraint Programming . dead . INFORMS Journal on Computing . 14 . 4 . 322–344 . 10.1.1.8.9699 . 10.1287/ijoc.14.4.322.2825 . https://web.archive.org/web/20200730181616/https://pubsonline.informs.org/doi/abs/10.1287/ijoc.14.4.322.2825 . Jul 30, 2020.
4. Web site: Netlib/Ampl.
5. Web site: Ampl/Mp. GitHub. 10 April 2022.