sif-rs

A Rust parser for the Standard Input Format (SIF) used in mathematical optimization.

SIF is a fixed-width text format for describing optimization problems such as linear programs (LP) and quadratic programs (QP). It is closely related to the MPS format and is natively used by the CUTEst benchmark library.

Installation

Add to your Cargo.toml:

[dependencies]
sif-rs = { path = "path/to/sif-rs" }   # local checkout

File structure

A SIF file consists of named sections delimited by indicator cards — a keyword in column 1 on its own line. The body of each section contains data rows. Depending on the section, the first token of each data row may be a short type marker (e.g. N/G/L/E in ROWS, LO/UP/FX in BOUNDS) followed by up to two name–value pairs:

<marker>  <name1>   <name2>   <value1>  <name3>   <value2>

For example, a COLUMNS entry (no marker):

    c1        r1                 2.0   r2                -1.0

And a ROWS entry (single-letter marker):

 G  r1

Lines beginning with * are comments and are ignored.

Usage

Parse a file directly from disk:

let sif = sif_rs::parse_file("examples/qptest.sif").unwrap();

Or supply an already-loaded string:

let input = std::fs::read_to_string("examples/qptest.sif").unwrap();
let sif = sif_rs::parse_sif(&input).unwrap();

Both functions return a SIF value containing the parsed problem data. The SIF type is currently opaque — its fields are not yet part of the public API. This will change in a future release.

Supported sections

Section	Aliases	Description
NAME	—	Problem name
ROWS	GROUPS, CONSTRAINTS	Constraint/row definitions
COLUMNS	VARIABLES	Variable-to-row coefficient entries
RHS	CONSTANTS, RHS'	Right-hand side values
RANGES	—	Range values for constraints (stub)
BOUNDS	—	Variable bounds
START POINT	—	Warm-start variable values (stub)
QUADRATIC	HESSIAN, QUADS, QUADOBJ, QSECTION	Quadratic objective terms
ELEMENT TYPE	—	Nonlinear element-type definitions (stub)
ELEMENT USES	—	Nonlinear element instantiations (stub)
GROUP TYPE	—	Nonlinear group-type definitions (stub)
GROUP USES	—	Nonlinear group instantiations (stub)
OBJECT BOUNDS	—	Known bounds on the objective value (stub)
ENDATA	—	End-of-file marker

Sections marked stub are recognized but their data is not yet stored or returned.

Known limitations

• Column-major ordering — files where COLUMNS/VARIABLES appears before ROWS/GROUPS are not yet supported. Row-major ordering (the common case) works correctly.
• LANCELOT nonlinear sections — ELEMENT TYPE, ELEMENT USES, GROUP TYPE, GROUP USES, and OBJECT BOUNDS are parsed as stubs; their data is discarded.
• RANGES and START POINT are similarly stubbed out.

Row types

Type	Meaning
N	Free row — typically the objective function
G	Greater-than-or-equal (≥) constraint
L	Less-than-or-equal (≤) constraint
E	Equality (=) constraint

Bound types

Type	Meaning
LO	Lower bound
UP	Upper bound
FX	Fixed value (lower = upper)
FR	Free variable (no bounds)
MI	Lower bound of −∞
PL	Upper bound of +∞ (default)

License

See LICENSE.

---

AI disclaimer: The documentation in this repository (README and inline doc comments) was generated with the assistance of Claude (Anthropic). Code logic and structure were written by the project author.