What is "nl"

NL may stand for:

nl is a Unix utility for numbering lines, either from a file or from standard input, reproducing output on standard output.

It has a number of switches:

• a - number all lines
• t - number lines with printable text only
• n - no line numbering
• string - number only those lines containing the regular expression defined in the string supplied.

The default applied switch is t.

nl also supports a number of command line options.

In computational complexity theory, NL (Nondeterministic Logarithmic-space) is the complexity class containing decision problems which can be solved by a nondeterministic Turing machine using a logarithmic amount of memory space.

NL is a generalization of L, the class for logspace problems on a deterministic Turing machine. Since any deterministic Turing machine is also a nondeterministic Turing machine, we have that L is contained in NL.

NL can be formally defined in terms of the computational resource nondeterministic space (or NSPACE) as NL = NSPACE(log n).

Important results in complexity theory allow us to relate this complexity class with other classes, telling us about the relative power of the resources involved. Results in the field of algorithms, on the other hand, tell us which problems can be solved with this resource. Like much of complexity theory, many important questions about NL are still open (see Unsolved problems in computer science).

Occasionally NL is referred to as RL due to its probabilistic definition below; however, this name is more frequently used to refer to randomized logarithmic space, which is not known to equal NL.

nl is a file format for presenting and archiving mathematical programming problems. Initially this format has been invented for connecting solvers to AMPL. 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

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 open-source AMPL Solver Library (ASL) distributed via Netlib and AMPL/MP library provide nl parsers that are used in many solvers.