nl (format)

Nl (format)

Filename extension	.nl
Developed by	Robert Fourer David Gay Brian Kernighan Bell Labs
Type of format	mathematical programming

nl is a file format for presenting and archiving mathematical programming problems^[1]. It supports linear and nonlinear optimization problems as well as complementarity problems (MPECs), in discrete or continuous variables. Initially this format has been invented for connecting solvers to AMPL^[2] but then it has been adopted by other systems such as COIN-OR as one of the input formats and FortSP for interacting with external solvers.

The nl format is low-level and is designed for compactness not for readability. It has both binary and textual representation. Many solvers such as CPLEX, Gurobi and MOSEK accept this format either directly or through special driver programs.

The AMPL Solver Library (ASL) which allows to read the nl files and provides the automatic differentiation functionality is open-source. It is used in many solvers to implement AMPL connection.

References

1. ^ David Gay (2005) (PDF). Writing .nl Files (Technical report). Sandia National Laboratories. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.60.9659&rep=rep1&type=pdf. 
2. ^ David Gay (1993) (PDF). Hooking Your Solver to AMPL (Technical report). Bell Laboratories. 97-4-06. http://www.ampl.com/REFS/hooking2.pdf. 

See Also

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