def METHOD_NAME(A, b, lower=False, x0=None):
    """
    Solve the linear system using a Cholesky Factorisation.
    The diagonal shift on the matrix should be 0.
    Internally uses {ref}`jax.numpy.linalg.cho_solve`.
    Args:
        A: the matrix A in Ax=b
        b: the vector b in Ax=b
        lower: if True uses the lower half of the A matrix
        x0: unused
    """
    del x0
    A = A.to_dense()
    b, unravel = tree_ravel(b)
    c, low = jsp.linalg.cho_factor(A, lower=lower)
    x = jsp.linalg.cho_solve((c, low), b)
    return unravel(x), None