matrixmania/compute.py

import math

from tabulate import tabulate


def matmul(a: list[list[float]], b: list[list[float]]) -> list[list[float]]:
    """Multiplicates two matrices.

    Parameters
    ----------
    a : list[list[float]]
        Left matrix in row‑major order.
    b : list[list[float]]
        Right matrix in row‑major order.

    Returns
    -------
    list[list[float]]
        Product matrix `c = a × b`.

    Raises
    ------
    ValueError
        If matrices are not rectangular or if the number of columns in ``a``
        does not equal the number of rows in ``b``.

    Notes
    -----
    * Empty matrices (``[]``) yield an empty result.
    * The implementation uses pure Python lists and does not depend on
      external libraries such as NumPy.
    """
    # Validate input matrices are non‑empty lists of lists
    if not isinstance(a, list) or not isinstance(b, list):
        raise ValueError("Both arguments must be lists of lists.")

    # Handle empty matrices early – return empty list for any empty input
    if not a or not b:
        return []

    # Determine dimensions of left matrix ``a``
    a_rows = len(a)
    a_cols = None
    for row in a:
        if not isinstance(row, list):
            raise ValueError("Matrix a must be a list of lists.")
        if a_cols is None:
            a_cols = len(row)
        elif len(row) != a_cols:
            raise ValueError("All rows in matrix a must have the same length.")

    # Determine dimensions of right matrix ``b``
    b_rows = len(b)
    b_cols = None
    for row in b:
        if not isinstance(row, list):
            raise ValueError("Matrix b must be a list of lists.")
        if b_cols is None:
            b_cols = len(row)
        elif len(row) != b_cols:
            raise ValueError("All rows in matrix b must have the same length.")

    # Check for dimensional compatibility between ``a`` and ``b``
    if a_cols != b_rows:
        raise ValueError(
            f"Matrix dimensions do not align: a.columns={a_cols} != b.rows={b_rows}"
        )

    # Initialize result matrix with zeros – dimensions a_rows × b_cols
    result = [[0.0 for _ in range(b_cols)] for _ in range(a_rows)]

    # Perform multiplication: iterate over rows of ``a`` and columns of ``b``
    for i in range(a_rows):
        for j in range(b_cols):
            s = 0.0
            for k in range(a_cols):
                s += a[i][k] * b[k][j]
            result[i][j] = s

    return result


def transpose(a: list[list[float]]) -> list[list[float]]:
    """Transposes a matrix.

    Parameters
    ----------
    a : list[list[float]]
        Matrix in row‑major order.

    Returns
    -------
    list[list[float]]
        Transposed matrix where rows and columns are swapped.

    Raises
    ------
    ValueError
        If the matrix is not rectangular.

    Notes
    -----
    * Empty matrices (``[]``) yield an empty result.
    * The implementation uses pure Python lists and does not depend on
      external libraries such as NumPy.
    """
    # Validate input is a list
    if not isinstance(a, list):
        raise ValueError("Argument must be a list of lists.")

    # Handle empty matrix early – return empty list
    if not a:
        return []

    # Determine dimensions and check rectangularity
    rows = len(a)
    cols = None
    for row in a:
        if not isinstance(row, list):
            raise ValueError("Matrix must be a list of lists.")
        if cols is None:
            cols = len(row)
        elif len(row) != cols:
            raise ValueError("All rows in the matrix must have the same length.")

    # Build transposed matrix with dimensions cols × rows
    result = [[a[i][j] for i in range(rows)] for j in range(cols)]

    return result


def rot_2D(angle: float) -> list[list[float]]:
    """Creates a 2×2 rotation matrix.

    Parameters
    ----------
    angle : float
        Rotation angle in radians (counter‑clockwise).

    Returns
    -------
    list[list[float]]
        Matrix ``[[cos(angle), -sin(angle)], [sin(angle), cos(angle)]]``.

    Raises
    ------
    ValueError
        If ``angle`` is not a real number.

    Notes
    -----
    * The implementation uses pure Python lists and does not depend on
      external libraries such as NumPy.
    """
    # Validate input is a real number
    if not isinstance(angle, (int, float)) or isinstance(angle, bool):
        raise ValueError("Angle must be a real number (radians).")

    c = math.cos(angle)
    s = math.sin(angle)

    return [[c, -s], [s, c]]


if __name__ == "__main__":
    # Beispiel 1: 2x3 × 3x2
    a = [[1, 2, 3], [4, 5, 6]]
    b = [[7, 8], [9, 10], [11, 12]]
    print("Beispiel 1 Ergebnis:")
    for row in matmul(a, b):
        print(row)

    # Beispiel 2: 2x2 × 2x2
    a2 = [[1, 0], [0, 1]]
    b2 = [[5, 6], [7, 8]]
    print("\nBeispiel 2 Ergebnis:")
    for row in matmul(a2, b2):
        print(row)

    # Beispiel 3: Transponieren einer 2x3-Matrix -> 3x2
    m = [[1, 2, 3], [4, 5, 6]]
    print("\nBeispiel 3 Original:")
    for row in m:
        print(row)
    print("Beispiel 3 Transponiert:")
    for row in transpose(m):
        print(row)

    # Beispiel 4: Rotationsmatrix (90°) und Probe durch Drehen von (1, 0)
    r = rot_2D(math.pi / 2)
    print("\nBeispiel 4 Rotationsmatrix (90°):")
    for row in r:
        print(row)
    print("Beispiel 4 Vektor (1, 0) nach 90°:")
    for row in matmul(r, [[1.0], [0.0]]):
        print([round(v, 10) for v in row])

    # Matrix in Tabelle ausgeben
    print(tabulate(rot_2D(1.0)))

# Docstring und Type Hints sind vorhanden und stimmen mit dem Code überein.
# Fehlerfälle werden behandelt
# Namen sind Aussagekräftig