Rust LP File Parser, Writer, and Diff Tool

Overview

A robust Rust library for parsing, modifying, and writing Linear Programming (LP) files. Built on the LALRPOP parser generator, this crate provides comprehensive support for the LP file format with the ability to parse, programmatically modify, and regenerate LP files according to major industry specifications.

The Grammar is defined with the lp.lalrpop file - should you be curious...

Supported Specifications

• IBM CPLEX v22.1.1
• FICO Xpress
• Gurobi
• Mosek

Features

Core Functionality

• Problem Definition

  • Problem name and sense specification
  • Single and multi-objective optimisation support
  • Comprehensive constraint handling

• Variable Support

  • Integer, general, bounded, free, semi-continuous variables

• LP File Writing and Modification

  • Generate LP files from parsed problems
  • Modify objectives, constraints, and variables programmatically
  • Round-trip compatibility (parse → modify → write → parse)
  • Maintain proper LP format specifications

Advanced Features

• LP File Comparison (diff feature)

  • Identify added, removed, and modified elements
  • Useful for model version control and validation

• Serialisation (serde feature)

  • Full serialisation support for all model structures
  • Compatible with various data formats
  • Enables integration with other tools and systems

Quick Start

Installation

Add to your Cargo.toml:

[dependencies]
lp_parser_rs = "3.0.0" # x-release-please-version

Basic Usage

Using the library directly:

use lp_parser_rs::{parser::parse_file, problem::LpProblem};
use std::path::Path;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Parse LP file content
    let content = parse_file(Path::new("problem.lp"))?;

    // Parse into LP problem structure
    let problem = LpProblem::parse(&content)?;

    // Access problem components
    println!("Problem name: {:?}", problem.name());
    println!("Objective count: {}", problem.objective_count());
    println!("Constraint count: {}", problem.constraint_count());
    println!("Variable count: {}", problem.variable_count());

    Ok(())
}

LP File Writing and Modification

use lp_parser_rs::{problem::LpProblem, writer::write_lp_string, model::*};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Parse an existing LP file
    let lp_content = std::fs::read_to_string("problem.lp")?;
    let mut problem = LpProblem::parse(&lp_content)?;

    // Modify objectives
    problem.update_objective_coefficient("profit", "x1", 5.0)?;
    problem.rename_objective("profit", "total_profit")?;

    // Modify constraints
    problem.update_constraint_coefficient("capacity", "x1", 2.0)?;
    problem.update_constraint_rhs("capacity", 200.0)?;
    problem.rename_constraint("capacity", "production_limit")?;

    // Modify variables
    problem.rename_variable("x1", "production_a")?;
    problem.update_variable_type("production_a", VariableType::Integer)?;

    // Write back to LP format
    let modified_lp = write_lp_string(&problem)?;
    std::fs::write("modified_problem.lp", modified_lp)?;

    Ok(())
}

Enable Optional Features

[dependencies]
lp_parser_rs = { version = "3.0.0", features = ["serde", "diff"] } # x-release-please-version

Command-Line Interface

The lp_parser binary provides a comprehensive CLI for working with LP files.

Installation

# Install with all features
cargo install lp_parser_rs --all-features

# Or build from source
git clone https://github.com/dandxy89/lp_parser_rs.git
cd lp_parser_rs/rust
cargo build --release --all-features

Commands

lp_parser <COMMAND>

Commands:
  parse    Parse an LP file and display its structure
  info     Show detailed statistics about an LP problem
  diff     Compare two LP files (requires 'diff' feature)
  convert  Convert LP file to another format
  solve    Solve an LP problem using external solvers (requires 'lp-solvers' feature)

Global Options:
  -v, --verbose    Increase output verbosity
  -q, --quiet      Suppress non-essential output
  -h, --help       Print help
  -V, --version    Print version

Examples

Parse and display an LP file:

lp_parser parse problem.lp

Get problem statistics:

lp_parser info problem.lp
# With detailed listings
lp_parser info problem.lp --variables --constraints --objectives

Output as JSON or YAML:

lp_parser info problem.lp --format json --pretty
lp_parser parse problem.lp --format yaml -o problem.yaml

Compare two LP files:

lp_parser diff old_model.lp new_model.lp
lp_parser diff old.lp new.lp --format json --pretty

Convert between formats:

# To LP (with formatting options)
lp_parser convert problem.lp --format lp --precision 4 --compact

# To CSV (creates constraints.csv, objectives.csv, variables.csv)
lp_parser convert problem.lp --format csv --output ./output_dir

# To JSON/YAML
lp_parser convert problem.lp --format json --pretty -o problem.json
lp_parser convert problem.lp --format yaml -o problem.yaml

Solve with external solvers:

# Using CBC (default)
lp_parser solve problem.lp

# Using GLPK
lp_parser solve problem.lp --solver glpk

# Output solution as JSON
lp_parser solve problem.lp --format json --pretty

Solving with External Solvers (lp-solvers feature)

Enable the lp-solvers feature to solve parsed LP problems using external solvers like CBC, Gurobi, CPLEX, or GLPK via the lp-solvers crate:

[dependencies]
lp_parser_rs = { version = "3.0.0", features = ["lp-solvers"] } # x-release-please-version
lp-solvers = "1.1"

use lp_parser_rs::{problem::LpProblem, ToLpSolvers};
use lp_solvers::solvers::{CbcSolver, SolverTrait};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let lp_content = r"
Minimize
 obj: 2 x + 3 y
Subject To
 c1: x + y <= 10
 c2: x >= 2
Bounds
 x >= 0
 y >= 0
End
";

    let problem = LpProblem::parse(lp_content)?;
    let compat = problem.to_lp_solvers()?;

    // Check for any compatibility warnings
    for warning in compat.warnings() {
        eprintln!("Warning: {}", warning);
    }

    // Solve using CBC solver (must be installed on your system)
    let solver = CbcSolver::new();
    let solution = solver.run(&compat)?;
    println!("Solution status: {:?}", solution.status);

    Ok(())
}

Limitations: The lp-solvers compatibility layer does not support multiple objectives (returns an error), strict inequalities (<, >), or SOS constraints (ignored with a warning).

API Reference

Problem Modification Methods

The LpProblem struct provides comprehensive methods for modifying LP problems:

Objective Modifications

• update_objective_coefficient(objective_name, variable_name, coefficient) - Update or add a coefficient in an objective
• rename_objective(old_name, new_name) - Rename an objective
• remove_objective(objective_name) - Remove an objective

Constraint Modifications

• update_constraint_coefficient(constraint_name, variable_name, coefficient) - Update or add a coefficient in a constraint
• update_constraint_rhs(constraint_name, new_rhs) - Update the right-hand side value
• rename_constraint(old_name, new_name) - Rename a constraint
• remove_constraint(constraint_name) - Remove a constraint

Variable Modifications

• rename_variable(old_name, new_name) - Rename a variable across all objectives and constraints
• update_variable_type(variable_name, new_type) - Change variable type (Binary, Integer, etc.)
• remove_variable(variable_name) - Remove a variable from all objectives and constraints

Writing LP Files

use lp_parser_rs::writer::{write_lp_string, write_lp_string_with_options, LpWriterOptions};

// Write with default options
let lp_content = write_lp_string(&problem)?;

// Write with custom options
let options = LpWriterOptions {
    include_problem_name: true,
    max_line_length: 80,
    decimal_precision: 6,
    include_section_spacing: true,
};
let lp_content = write_lp_string_with_options(&problem, &options)?;

Development

Testing

The project uses snapshot testing via insta for reliable test management:

# Run all tests with all features enabled
cargo insta test --all-features

# Review snapshot changes
cargo insta review

Test Data Sources

The test suite includes data from various open-source projects:

• Jplex
• LPWriter.jl
• Lp-Parser

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.