qec-code 0.3.0

Rust primitives for constructing and analyzing quantum error-correcting codes
Documentation 
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use qec_code::sparse_gf2::{hconcat, identity, kron, transpose, SparseGf2Matrix};
use qec_code::QecError;

fn assert_shape_and_rows(
    matrix: &SparseGf2Matrix,
    num_rows: usize,
    num_cols: usize,
    rows: &[Vec<usize>],
) {
    assert_eq!(matrix.num_rows(), num_rows);
    assert_eq!(matrix.num_cols(), num_cols);
    assert_eq!(matrix.rows(), rows);
}

#[test]
fn sparse_gf2_composition_matches_known_answers() {
    let a = SparseGf2Matrix::new(2, 2, vec![vec![0], vec![0, 1]]).unwrap();
    let b = SparseGf2Matrix::new(2, 2, vec![vec![1], vec![0]]).unwrap();

    assert_shape_and_rows(&identity(2).unwrap(), 2, 2, &[vec![0], vec![1]]);
    assert_shape_and_rows(&transpose(&a).unwrap(), 2, 2, &[vec![0, 1], vec![1]]);
    assert_shape_and_rows(
        &hconcat(&a, &b).unwrap(),
        2,
        4,
        &[vec![0, 3], vec![0, 1, 2]],
    );
    assert_shape_and_rows(
        &kron(&a, &b).unwrap(),
        4,
        4,
        &[vec![1], vec![0], vec![1, 3], vec![0, 2]],
    );

    let canonicalized = SparseGf2Matrix::new(2, 4, vec![vec![3, 1, 3, 2, 1], vec![2, 2]]).unwrap();
    assert_shape_and_rows(&canonicalized, 2, 4, &[vec![2], vec![]]);

    assert_shape_and_rows(&identity(0).unwrap(), 0, 0, &[]);

    let empty_wide = SparseGf2Matrix::new(0, 3, vec![]).unwrap();
    assert_shape_and_rows(
        &transpose(&empty_wide).unwrap(),
        3,
        0,
        &[vec![], vec![], vec![]],
    );

    let empty_rows_left = SparseGf2Matrix::new(0, 2, vec![]).unwrap();
    let empty_rows_right = SparseGf2Matrix::new(0, 5, vec![]).unwrap();
    assert_shape_and_rows(
        &hconcat(&empty_rows_left, &empty_rows_right).unwrap(),
        0,
        7,
        &[],
    );
    assert_shape_and_rows(
        &kron(&empty_rows_left, &empty_rows_right).unwrap(),
        0,
        10,
        &[],
    );
}

#[test]
fn sparse_gf2_methods_cover_rectangular_composition() {
    let left = SparseGf2Matrix::new(2, 3, vec![vec![0, 2], vec![1]]).unwrap();
    let right = SparseGf2Matrix::new(2, 1, vec![vec![0], vec![]]).unwrap();
    let factor = SparseGf2Matrix::new(1, 2, vec![vec![1]]).unwrap();

    assert_shape_and_rows(
        &SparseGf2Matrix::identity(3).unwrap(),
        3,
        3,
        &[vec![0], vec![1], vec![2]],
    );
    assert_shape_and_rows(
        &left.transpose().unwrap(),
        3,
        2,
        &[vec![0], vec![1], vec![0]],
    );
    assert_shape_and_rows(
        &left.hconcat(&right).unwrap(),
        2,
        4,
        &[vec![0, 2, 3], vec![1]],
    );
    assert_shape_and_rows(&left.kron(&factor).unwrap(), 2, 6, &[vec![1, 5], vec![3]]);
}

#[test]
fn sparse_gf2_composition_rejects_invalid_shapes() {
    assert_eq!(
        SparseGf2Matrix::new(1, 2, vec![vec![2]]),
        Err(QecError::SparseGf2SupportOutOfRange {
            row: 0,
            support: 2,
            num_cols: 2,
        })
    );

    assert_eq!(
        SparseGf2Matrix::new(2, 2, vec![vec![]]),
        Err(QecError::SparseGf2RowCountMismatch {
            expected: 2,
            actual: 1,
        })
    );

    let one_row = SparseGf2Matrix::new(1, 2, vec![vec![0]]).unwrap();
    let two_rows = SparseGf2Matrix::new(2, 2, vec![vec![0], vec![1]]).unwrap();
    assert_eq!(
        hconcat(&one_row, &two_rows),
        Err(QecError::SparseGf2HorizontalRowMismatch {
            left_rows: 1,
            right_rows: 2,
        })
    );

    let max_width = SparseGf2Matrix::new(0, usize::MAX, vec![]).unwrap();
    let one_col = SparseGf2Matrix::new(0, 1, vec![]).unwrap();
    assert_eq!(
        hconcat(&max_width, &one_col),
        Err(QecError::SparseGf2DimensionOverflow {
            operation: "hconcat",
        })
    );

    let two_cols = SparseGf2Matrix::new(0, 2, vec![]).unwrap();
    assert_eq!(
        kron(&max_width, &two_cols),
        Err(QecError::SparseGf2DimensionOverflow { operation: "kron" })
    );
}

#[test]
fn sparse_gf2_composition_reports_reachable_allocation_overflows() {
    assert_eq!(
        SparseGf2Matrix::identity(usize::MAX),
        Err(QecError::SparseGf2DimensionOverflow {
            operation: "identity",
        })
    );

    let max_width = SparseGf2Matrix::new(0, usize::MAX, vec![]).unwrap();
    assert_eq!(
        max_width.transpose(),
        Err(QecError::SparseGf2DimensionOverflow {
            operation: "transpose",
        })
    );
}