main.rs

//! Implementation of an expansion-contraction algorithm to find wheel cohomology classes in the graph complex.

mod expand_n_contract;
mod expand_n_contract_sqlite;
mod undirected_graph;
use std::env;
use std::process;

/// Parses and checks command line arguments; runs the expansion-contraction algorithm.
fn main() -> std::io::Result<()> {
    let args: Vec<String> = env::args().collect();
    let num_args: usize = args.len();

    const NUM_ARGS_FOR_DB: usize = 3;
    const NUM_ARGS_FOR_TXT: usize = 5;

    if num_args != NUM_ARGS_FOR_DB && num_args != NUM_ARGS_FOR_TXT {
        eprintln!(
            "Usage:\n\
            \x20 {} <number-of-spokes-in-wheel> <output-filename.db>\n\
            or\n\
            \x20 {} <number-of-spokes-in-wheel> <cocycle-graphs.txt> <cocycle-differential-graphs.txt> <cocycle-differential-matrix.txt>",
            args[0], args[0]
        );
        process::exit(1);
    }

    let num_spokes_maybe: Result<usize, std::num::ParseIntError> = args[1].parse::<usize>();
    if num_spokes_maybe.is_err() {
        eprintln!("Error parsing the first argument as a natural number.");
        process::exit(1);
    }
    let num_spokes: usize = num_spokes_maybe.unwrap();

    if num_spokes < 2 {
        eprintln!("Error: A wheel graph without tadpoles must have at least two spokes.");
        process::exit(1);
    }

    if num_spokes % 2 == 0 {
        eprintln!("Error: The {}-wheel graph has an automorphism that induces an odd permutation on edges, so it is equal to zero in the graph complex.", num_spokes);
        process::exit(1);
    }

    if num_args == NUM_ARGS_FOR_DB {
        let filename: &String = &args[2];

        let result: Result<(usize, usize, usize), rusqlite::Error> =
            expand_n_contract_sqlite::expand_n_contract(num_spokes, filename);

        match result {
            Ok((num_rows, num_columns, num_nonzeros)) => {
                eprintln!(
                    "Sparse {} x {} matrix with {} non-zero entries",
                    num_rows, num_columns, num_nonzeros
                );
                Ok(())
            }
            Err(e) => {
                eprintln!("{}", e);
                Err(std::io::Error::new(
                    std::io::ErrorKind::Other,
                    "Database error",
                ))
            }
        }
    } else if num_args == NUM_ARGS_FOR_TXT {
        let cocycle_graphs_filename: &String = &args[2];
        let cocycle_differential_graphs_filename: &String = &args[3];
        let cocycle_differential_matrix_filename: &String = &args[4];

        let result: Result<(usize, usize, usize), std::io::Error> =
            expand_n_contract::expand_n_contract(
                num_spokes,
                cocycle_graphs_filename,
                cocycle_differential_graphs_filename,
                cocycle_differential_matrix_filename,
            );

        match result {
            Ok((num_rows, num_columns, num_nonzeros)) => {
                eprintln!(
                    "Sparse {} x {} matrix with {} non-zero entries",
                    num_rows, num_columns, num_nonzeros
                );
                Ok(())
            }
            Err(e) => Err(e),
        }
    } else {
        Err(std::io::Error::new(
            std::io::ErrorKind::InvalidInput,
            "File extension not recognized.",
        ))
    }
}