rationaltools.py 文件源码

def ratint_ratpart(f, g, x):
    """
    Horowitz-Ostrogradsky algorithm.

    Given a field K and polynomials f and g in K[x], such that f and g
    are coprime and deg(f) < deg(g), returns fractions A and B in K(x),
    such that f/g = A' + B and B has square-free denominator.

    Examples
    ========

        >>> from sympy.integrals.rationaltools import ratint_ratpart
        >>> from sympy.abc import x, y
        >>> from sympy import Poly
        >>> ratint_ratpart(Poly(1, x, domain='ZZ'),
        ... Poly(x + 1, x, domain='ZZ'), x)
        (0, 1/(x + 1))
        >>> ratint_ratpart(Poly(1, x, domain='EX'),
        ... Poly(x**2 + y**2, x, domain='EX'), x)
        (0, 1/(x**2 + y**2))
        >>> ratint_ratpart(Poly(36, x, domain='ZZ'),
        ... Poly(x**5 - 2*x**4 - 2*x**3 + 4*x**2 + x - 2, x, domain='ZZ'), x)
        ((12*x + 6)/(x**2 - 1), 12/(x**2 - x - 2))

    See Also
    ========

    ratint, ratint_logpart
    """
    from sympy import solve

    f = Poly(f, x)
    g = Poly(g, x)

    u, v, _ = g.cofactors(g.diff())

    n = u.degree()
    m = v.degree()

    A_coeffs = [ Dummy('a' + str(n - i)) for i in range(0, n) ]
    B_coeffs = [ Dummy('b' + str(m - i)) for i in range(0, m) ]

    C_coeffs = A_coeffs + B_coeffs

    A = Poly(A_coeffs, x, domain=ZZ[C_coeffs])
    B = Poly(B_coeffs, x, domain=ZZ[C_coeffs])

    H = f - A.diff()*v + A*(u.diff()*v).quo(u) - B*u

    result = solve(H.coeffs(), C_coeffs)

    A = A.as_expr().subs(result)
    B = B.as_expr().subs(result)

    rat_part = cancel(A/u.as_expr(), x)
    log_part = cancel(B/v.as_expr(), x)

    return rat_part, log_part