Python miscellaneous.root函数代码示例

def roots_cubic(f, trig=False):
    """Returns a list of roots of a cubic polynomial."""
    if trig:
        a, b, c, d = f.all_coeffs()
        p = (3*a*c - b**2)/3/a**2
        q = (2*b**3 - 9*a*b*c + 27*a**2*d)/(27*a**3)
        D = 18*a*b*c*d - 4*b**3*d + b**2*c**2 - 4*a*c**3 - 27*a**2*d**2
        if (D > 0) == True:
            rv = []
            for k in range(3):
                rv.append(2*sqrt(-p/3)*cos(acos(3*q/2/p*sqrt(-3/p))/3 - k*2*pi/3))
            return [i - b/3/a for i in rv]

    _, a, b, c = f.monic().all_coeffs()

    if c is S.Zero:
        x1, x2 = roots([1, a, b], multiple=True)
        return [x1, S.Zero, x2]

    p = b - a**2/3
    q = c - a*b/3 + 2*a**3/27

    pon3 = p/3
    aon3 = a/3

    if p is S.Zero:
        if q is S.Zero:
            return [-aon3]*3
        else:
            if q.is_real:
                if (q > 0) == True:
                    u1 = -root(q, 3)
                else:
                    u1 = root(-q, 3)
            else:
                u1 = root(-q, 3)
    elif q is S.Zero:
        y1, y2 = roots([1, 0, p], multiple=True)
        return [tmp - aon3 for tmp in [y1, S.Zero, y2]]
    elif q.is_real and q < 0:
        u1 = -root(-q/2 + sqrt(q**2/4 + pon3**3), 3)
    else:
        u1 = root(q/2 + sqrt(q**2/4 + pon3**3), 3)

    coeff = I*sqrt(3)/2

    u2 = u1*(-S.Half + coeff)
    u3 = u1*(-S.Half - coeff)

    if p is S.Zero:
        return [u1 - aon3, u2 - aon3, u3 - aon3]

    soln = [
        -u1 + pon3/u1 - aon3,
        -u2 + pon3/u2 - aon3,
        -u3 + pon3/u3 - aon3
    ]

    return soln

def test_nthroot():
    assert real_root(-8, 3) == -2
    assert real_root(-16, 4) == root(-16, 4)
    r = root(-7, 4)
    assert real_root(r) == r
    r1 = root(-1, 3)
    r2 = r1**2
    r3 = root(-1, 4)
    assert real_root(r1 + r2 + r3) == -1 + r2 + r3

def test_issue_14000():
    assert isinstance(sqrt(4, evaluate=False), Pow) == True
    assert isinstance(cbrt(3.5, evaluate=False), Pow) == True
    assert isinstance(root(16, 4, evaluate=False), Pow) == True

    assert sqrt(4, evaluate=False) == Pow(4, S.Half, evaluate=False)
    assert cbrt(3.5, evaluate=False) == Pow(3.5, Rational(1, 3), evaluate=False)
    assert root(4, 2, evaluate=False) == Pow(4, Rational(1, 2), evaluate=False)

    assert root(16, 4, 2, evaluate=False).has(Pow) == True
    assert real_root(-8, 3, evaluate=False).has(Pow) == True

 def taylor_term(n, x, *previous_terms):
     if n < 0:
         return S.Zero
     else:
         x = sympify(x)
         if len(previous_terms) > 1:
             p = previous_terms[-1]
             return (3**(S(1)/3)*x * Abs(sin(2*pi*(n + S.One)/S(3))) * C.factorial((n - S.One)/S(3)) /
                     ((n + S.One) * Abs(cos(2*pi*(n + S.Half)/S(3))) * C.factorial((n - 2)/S(3))) * p)
         else:
             return (S.One/(root(3, 6)*pi) * gamma((n + S.One)/S(3)) * Abs(sin(2*pi*(n + S.One)/S(3))) /
                     C.factorial(n) * (root(3, 3)*x)**n)

def roots_cyclotomic(f, factor=False):
    """Compute roots of cyclotomic polynomials. """
    L, U = _inv_totient_estimate(f.degree())

    for n in range(L, U + 1):
        g = cyclotomic_poly(n, f.gen, polys=True)

        if f == g:
            break
    else:  # pragma: no cover
        raise RuntimeError("failed to find index of a cyclotomic polynomial")

    roots = []

    if not factor:
        # get the indices in the right order so the computed
        # roots will be sorted
        h = n//2
        ks = [i for i in range(1, n + 1) if igcd(i, n) == 1]
        ks.sort(key=lambda x: (x, -1) if x <= h else (abs(x - n), 1))
        d = 2*I*pi/n
        for k in reversed(ks):
            roots.append(exp(k*d).expand(complex=True))
    else:
        g = Poly(f, extension=root(-1, n))

        for h, _ in ordered(g.factor_list()[1]):
            roots.append(-h.TC())

    return roots

def roots_cyclotomic(f, factor=False):
    """Compute roots of cyclotomic polynomials. """
    L, U = _inv_totient_estimate(f.degree())

    for n in xrange(L, U + 1):
        g = cyclotomic_poly(n, f.gen, polys=True)

        if f == g:
            break
    else:  # pragma: no cover
        raise RuntimeError("failed to find index of a cyclotomic polynomial")

    roots = []

    if not factor:
        for k in xrange(1, n + 1):
            if igcd(k, n) == 1:
                roots.append(exp(2*k*S.Pi*I/n).expand(complex=True))
    else:
        g = Poly(f, extension=root(-1, n))

        for h, _ in g.factor_list()[1]:
            roots.append(-h.TC())

    return sorted(roots, key=default_sort_key)

 def taylor_term(n, x, *previous_terms):
     if n < 0:
         return S.Zero
     else:
         x = sympify(x)
         if len(previous_terms) > 1:
             p = previous_terms[-1]
             return (
                 (3 ** (S(1) / 3) * x) ** (-n)
                 * (3 ** (S(1) / 3) * x) ** (n + 1)
                 * sin(pi * (2 * n / 3 + S(4) / 3))
                 * factorial(n)
                 * gamma(n / 3 + S(2) / 3)
                 / (sin(pi * (2 * n / 3 + S(2) / 3)) * factorial(n + 1) * gamma(n / 3 + S(1) / 3))
                 * p
             )
         else:
             return (
                 S.One
                 / (3 ** (S(2) / 3) * pi)
                 * gamma((n + S.One) / S(3))
                 * sin(2 * pi * (n + S.One) / S(3))
                 / factorial(n)
                 * (root(3, 3) * x) ** n
             )

def roots_binomial(f):
    """Returns a list of roots of a binomial polynomial. If the domain is ZZ
    then the roots will be sorted with negatives coming before positives.
    The ordering will be the same for any numerical coefficients as long as
    the assumptions tested are correct, otherwise the ordering will not be
    sorted (but will be canonical).
    """
    n = f.degree()

    a, b = f.nth(n), f.nth(0)
    base = -cancel(b/a)
    alpha = root(base, n)

    if alpha.is_number:
        alpha = alpha.expand(complex=True)

    # define some parameters that will allow us to order the roots.
    # If the domain is ZZ this is guaranteed to return roots sorted
    # with reals before non-real roots and non-real sorted according
    # to real part and imaginary part, e.g. -1, 1, -1 + I, 2 - I
    neg = base.is_negative
    even = n % 2 == 0
    if neg:
        if even == True and (base + 1).is_positive:
            big = True
        else:
            big = False

    # get the indices in the right order so the computed
    # roots will be sorted when the domain is ZZ
    ks = []
    imax = n//2
    if even:
        ks.append(imax)
        imax -= 1
    if not neg:
        ks.append(0)
    for i in range(imax, 0, -1):
        if neg:
            ks.extend([i, -i])
        else:
            ks.extend([-i, i])
    if neg:
        ks.append(0)
        if big:
            for i in range(0, len(ks), 2):
                pair = ks[i: i + 2]
                pair = list(reversed(pair))

    # compute the roots
    roots, d = [], 2*I*pi/n
    for k in ks:
        zeta = exp(k*d).expand(complex=True)
        roots.append((alpha*zeta).expand(power_base=False))

    return roots

def test_real_root():
    assert real_root(-8, 3) == -2
    assert real_root(-16, 4) == root(-16, 4)
    r = root(-7, 4)
    assert real_root(r) == r
    r1 = root(-1, 3)
    r2 = r1**2
    r3 = root(-1, 4)
    assert real_root(r1 + r2 + r3) == -1 + r2 + r3
    assert real_root(root(-2, 3)) == -root(2, 3)
    assert real_root(-8., 3) == -2

def test_real_root():
    assert real_root(-8, 3) == -2
    assert real_root(-16, 4) == root(-16, 4)
    r = root(-7, 4)
    assert real_root(r) == r
    r1 = root(-1, 3)
    r2 = r1**2
    r3 = root(-1, 4)
    assert real_root(r1 + r2 + r3) == -1 + r2 + r3
    assert real_root(root(-2, 3)) == -root(2, 3)
    assert real_root(-8., 3) == -2
    x = Symbol('x')
    n = Symbol('n')
    g = real_root(x, n)
    assert g.subs(dict(x=-8, n=3)) == -2
    assert g.subs(dict(x=8, n=3)) == 2
    # give principle root if there is no real root -- if this is not desired
    # then maybe a Root class is needed to raise an error instead
    assert g.subs(dict(x=I, n=3)) == cbrt(I)
    assert g.subs(dict(x=-8, n=2)) == sqrt(-8)
    assert g.subs(dict(x=I, n=2)) == sqrt(I)

 def _eval_rewrite_as_hyper(self, z):
     pf1 = z ** 2 / (2 * root(3, 6) * gamma(S(2) / 3))
     pf2 = root(3, 6) / gamma(S(1) / 3)
     return pf1 * hyper([], [S(5) / 3], z ** 3 / 9) + pf2 * hyper([], [S(1) / 3], z ** 3 / 9)

def roots_cubic(f, trig=False):
    """Returns a list of roots of a cubic polynomial.

    References
    ==========
    [1] https://en.wikipedia.org/wiki/Cubic_function, General formula for roots,
    (accessed November 17, 2014).
    """
    if trig:
        a, b, c, d = f.all_coeffs()
        p = (3*a*c - b**2)/3/a**2
        q = (2*b**3 - 9*a*b*c + 27*a**2*d)/(27*a**3)
        D = 18*a*b*c*d - 4*b**3*d + b**2*c**2 - 4*a*c**3 - 27*a**2*d**2
        if (D > 0) == True:
            rv = []
            for k in range(3):
                rv.append(2*sqrt(-p/3)*cos(acos(3*q/2/p*sqrt(-3/p))/3 - k*2*pi/3))
            return [i - b/3/a for i in rv]

    _, a, b, c = f.monic().all_coeffs()

    if c is S.Zero:
        x1, x2 = roots([1, a, b], multiple=True)
        return [x1, S.Zero, x2]

    p = b - a**2/3
    q = c - a*b/3 + 2*a**3/27

    pon3 = p/3
    aon3 = a/3

    u1 = None
    if p is S.Zero:
        if q is S.Zero:
            return [-aon3]*3
        if q.is_real:
            if q.is_positive:
                u1 = -root(q, 3)
            elif q.is_negative:
                u1 = root(-q, 3)
    elif q is S.Zero:
        y1, y2 = roots([1, 0, p], multiple=True)
        return [tmp - aon3 for tmp in [y1, S.Zero, y2]]
    elif q.is_real and q.is_negative:
        u1 = -root(-q/2 + sqrt(q**2/4 + pon3**3), 3)

    coeff = I*sqrt(3)/2
    if u1 is None:
        u1 = S(1)
        u2 = -S.Half + coeff
        u3 = -S.Half - coeff
        a, b, c, d = S(1), a, b, c
        D0 = b**2 - 3*a*c
        D1 = 2*b**3 - 9*a*b*c + 27*a**2*d
        C = root((D1 + sqrt(D1**2 - 4*D0**3))/2, 3)
        return [-(b + uk*C + D0/C/uk)/3/a for uk in [u1, u2, u3]]

    u2 = u1*(-S.Half + coeff)
    u3 = u1*(-S.Half - coeff)

    if p is S.Zero:
        return [u1 - aon3, u2 - aon3, u3 - aon3]

    soln = [
        -u1 + pon3/u1 - aon3,
        -u2 + pon3/u2 - aon3,
        -u3 + pon3/u3 - aon3
    ]

    return soln

def bivariate_type(f, x, y, **kwargs):
    """Given an expression, f, 3 tests will be done to see what type
    of composite bivariate it might be, options for u(x, y) are::

        x*y
        x+y
        x*y+x
        x*y+y

    If it matches one of these types, ``u(x, y)``, ``P(u)`` and dummy
    variable ``u`` will be returned. Solving ``P(u)`` for ``u`` and
    equating the solutions to ``u(x, y)`` and then solving for ``x`` or
    ``y`` is equivalent to solving the original expression for ``x`` or
    ``y``. If ``x`` and ``y`` represent two functions in the same
    variable, e.g. ``x = g(t)`` and ``y = h(t)``, then if ``u(x, y) - p``
    can be solved for ``t`` then these represent the solutions to
    ``P(u) = 0`` when ``p`` are the solutions of ``P(u) = 0``.

    Only positive values of ``u`` are considered.

    Examples
    ========

    >>> from sympy.solvers.solvers import solve
    >>> from sympy.solvers.bivariate import bivariate_type
    >>> from sympy.abc import x, y
    >>> eq = (x**2 - 3).subs(x, x + y)
    >>> bivariate_type(eq, x, y)
    (x + y, _u**2 - 3, _u)
    >>> uxy, pu, u = _
    >>> usol = solve(pu, u); usol
    [sqrt(3)]
    >>> [solve(uxy - s) for s in solve(pu, u)]
    [[{x: -y + sqrt(3)}]]
    >>> all(eq.subs(s).equals(0) for sol in _ for s in sol)
    True

    """

    u = Dummy('u', positive=True)

    if kwargs.pop('first', True):
        p = Poly(f, x, y)
        f = p.as_expr()
        _x = Dummy()
        _y = Dummy()
        rv = bivariate_type(Poly(f.subs({x: _x, y: _y}), _x, _y), _x, _y, first=False)
        if rv:
            reps = {_x: x, _y: y}
            return rv[0].xreplace(reps), rv[1].xreplace(reps), rv[2]
        return

    p = f
    f = p.as_expr()

    # f(x*y)
    args = Add.make_args(p.as_expr())
    new = []
    for a in args:
        a = _mexpand(a.subs(x, u/y))
        free = a.free_symbols
        if x in free or y in free:
            break
        new.append(a)
    else:
        return x*y, Add(*new), u

    def ok(f, v, c):
        new = _mexpand(f.subs(v, c))
        free = new.free_symbols
        return None if (x in free or y in free) else new

    # f(a*x + b*y)
    new = []
    d = p.degree(x)
    if p.degree(y) == d:
        a = root(p.coeff_monomial(x**d), d)
        b = root(p.coeff_monomial(y**d), d)
        new = ok(f, x, (u - b*y)/a)
        if new is not None:
            return a*x + b*y, new, u

    # f(a*x*y + b*y)
    new = []
    d = p.degree(x)
    if p.degree(y) == d:
        for itry in range(2):
            a = root(p.coeff_monomial(x**d*y**d), d)
            b = root(p.coeff_monomial(y**d), d)
            new = ok(f, x, (u - b*y)/a/y)
            if new is not None:
                return a*x*y + b*y, new, u
            x, y = y, x

def test_root():
    from sympy.abc import x

    n = Symbol("n", integer=True)
    k = Symbol("k", integer=True)

    assert root(2, 2) == sqrt(2)
    assert root(2, 1) == 2
    assert root(2, 3) == 2 ** Rational(1, 3)
    assert root(2, 3) == cbrt(2)
    assert root(2, -5) == 2 ** Rational(4, 5) / 2

    assert root(-2, 1) == -2

    assert root(-2, 2) == sqrt(2) * I
    assert root(-2, 1) == -2

    assert root(x, 2) == sqrt(x)
    assert root(x, 1) == x
    assert root(x, 3) == x ** Rational(1, 3)
    assert root(x, 3) == cbrt(x)
    assert root(x, -5) == x ** Rational(-1, 5)

    assert root(x, n) == x ** (1 / n)
    assert root(x, -n) == x ** (-1 / n)

    assert root(x, n, k) == x ** (1 / n) * (-1) ** (2 * k / n)

def test_root():
    from sympy.abc import x, y, z
    n = Symbol('n', integer=True)

    assert root(2, 2) == sqrt(2)
    assert root(2, 1) == 2
    assert root(2, 3) == 2**Rational(1,3)
    assert root(2, -5) == 2**Rational(4,5)/2

    assert root(-2, 1) == -2

    assert root(-2, 2) == sqrt(2)*I
    assert root(-2, 1) == -2

    assert root(x, 2) == sqrt(x)
    assert root(x, 1) == x
    assert root(x, 3) == x**Rational(1,3)
    assert root(x, -5) == x**Rational(-1,5)

    assert root(x, n) == x**(1/n)
    assert root(x, -n) == x**(-1/n)