TheAlgorithms/Python · error · Exception

Matrix is not square

Error message

Matrix is not square

What it means

Raised by Matrix.minor(x, y) in linear_algebra/src/lib.py:388 when the matrix is not square (height != width). A minor is the determinant of the submatrix obtained by deleting row x and column y, and the code immediately builds that submatrix and calls .determinant() — which also requires squareness — so non-square input is rejected up front with a bare Exception.

Source

Thrown at linear_algebra/src/lib.py:388

            return self.__matrix[x][y]
        else:
            raise Exception("change_component: indices out of bounds")

    def change_component(self, x: int, y: int, value: float) -> None:
        """
        changes the x-y component of this matrix
        """
        if 0 <= x < self.__height and 0 <= y < self.__width:
            self.__matrix[x][y] = value
        else:
            raise Exception("change_component: indices out of bounds")

    def minor(self, x: int, y: int) -> float:
        """
        returns the minor along (x, y)
        """
        if self.__height != self.__width:
            raise Exception("Matrix is not square")
        minor = self.__matrix[:x] + self.__matrix[x + 1 :]
        for i in range(len(minor)):
            minor[i] = minor[i][:y] + minor[i][y + 1 :]
        return Matrix(minor, self.__width - 1, self.__height - 1).determinant()

    def cofactor(self, x: int, y: int) -> float:
        """
        returns the cofactor (signed minor) along (x, y)
        """
        if self.__height != self.__width:
            raise Exception("Matrix is not square")
        if 0 <= x < self.__height and 0 <= y < self.__width:
            return (-1) ** (x + y) * self.minor(x, y)
        else:
            raise Exception("Indices out of bounds")

    def determinant(self) -> float:
        """

View on GitHub (pinned to f5988cc097)

Solutions

1. Check m.height() == m.width() before calling minor()/cofactor()/determinant().
2. Verify the (width, height) constructor arguments actually describe the nested list — swapped arguments make square data look rectangular.
3. For rectangular matrices, minors are undefined; compute rank/SVD or crop to a square submatrix explicitly if that is what you meant.
4. Catch Exception narrowly at boundaries.

Example fix

// before
m = Matrix([[1, 2, 3], [4, 5, 6]], 3, 2)
m.minor(0, 0)  # Exception: Matrix is not square

// after
assert m.height() == m.width(), f"minor needs a square matrix, got {m.height()}x{m.width()}"
m.minor(0, 0)

if m.height() != m.width():
    raise ValueError(f"minor requires a square matrix, got {m.height()}x{m.width()}")
value = m.minor(x, y)

from linear_algebra.src.lib import Matrix

def is_square_matrix(m) -> bool:
    return isinstance(m, Matrix) and m.height() == m.width()

try:
    value = m.minor(x, y)
except Exception as e:
    if "not square" in str(e):
        raise ValueError(f"cannot take minor of {m.height()}x{m.width()} matrix") from e
    raise

When it happens

Trigger: Calling minor() on any m x n Matrix with m != n, e.g. Matrix([[1, 2, 3], [4, 5, 6]], 3, 2).minor(0, 0). Typically hit while computing cofactors/determinants of rectangular data, or when the constructor's width/height arguments were swapped, making an intentionally square matrix rectangular.

Common situations: Feeding rectangular data tables into determinant-style computations, or dimension-argument mix-ups at Matrix construction (signature is (matrix, width, height)).

Related errors

• determinant modular {req_l} of encryption key({det}) is not
• 'table' has to be of square shaped array but got a {rows}x{c
• matrix must have the same dimension!
• matrices must have the same dimension!
• vector must have the same size as the number of columns of t

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/851cafce2e6ac78f. Report an issue: GitHub.