Esempio n. 1
0
def cancel_exp(b, c, n, DE):
    """
    Poly Risch Differential Equation - Cancellation: Hyperexponential case.

    Explanation
    ===========

    Given a derivation D on k[t], n either an integer or +oo, ``b`` in k, and
    ``c`` in k[t] with Dt/t in k and ``b != 0``, either raise
    NonElementaryIntegralException, in which case the equation Dq + b*q == c
    has no solution of degree at most n in k[t], or a solution q in k[t] of
    this equation with deg(q) <= n.
    """
    from sympy.integrals.prde import parametric_log_deriv

    eta = DE.d.quo(Poly(DE.t, DE.t)).as_expr()

    with DecrementLevel(DE):
        etaa, etad = frac_in(eta, DE.t)
        ba, bd = frac_in(b, DE.t)
        A = parametric_log_deriv(ba, bd, etaa, etad, DE)
        if A is not None:
            a, m, z = A
            if a == 1:
                raise NotImplementedError("is_deriv_in_field() is required to "
                    "solve this problem.")
                # if c*z*t**m == Dp for p in k<t> and q = p/(z*t**m) in k[t] and
                # deg(q) <= n:
                #     return q
                # else:
                #     raise NonElementaryIntegralException

    if c.is_zero:
        return c  # return 0

    if n < c.degree(DE.t):
        raise NonElementaryIntegralException

    q = Poly(0, DE.t)
    while not c.is_zero:
        m = c.degree(DE.t)
        if n < m:
            raise NonElementaryIntegralException
        # a1 = b + m*Dt/t
        a1 = b.as_expr()
        with DecrementLevel(DE):
            # TODO: Write a dummy function that does this idiom
            a1a, a1d = frac_in(a1, DE.t)
            a1a = a1a*etad + etaa*a1d*Poly(m, DE.t)
            a1d = a1d*etad

            a2a, a2d = frac_in(c.LC(), DE.t)

            sa, sd = rischDE(a1a, a1d, a2a, a2d, DE)
        stm = Poly(sa.as_expr()/sd.as_expr()*DE.t**m, DE.t, expand=False)
        q += stm
        n = m - 1
        c -= b*stm + derivation(stm, DE)  # deg(c) becomes smaller
    return q
Esempio n. 2
0
def cancel_exp(b, c, n, DE):
    """
    Poly Risch Differential Equation - Cancellation: Hyperexponential case.

    Given a derivation D on k[t], n either an integer or +oo, b in k, and
    c in k[t] with Dt/t in k and b != 0, either raise
    NonElementaryIntegralException, in which case the equation Dq + b*q == c
    has no solution of degree at most n in k[t], or a solution q in k[t] of
    this equation with deg(q) <= n.
    """
    from sympy.integrals.prde import parametric_log_deriv

    eta = DE.d.quo(Poly(DE.t, DE.t)).as_expr()

    with DecrementLevel(DE):
        etaa, etad = frac_in(eta, DE.t)
        ba, bd = frac_in(b, DE.t)
        A = parametric_log_deriv(ba, bd, etaa, etad, DE)
        if A is not None:
            a, m, z = A
            if a == 1:
                raise NotImplementedError("is_deriv_in_field() is required to "
                    "solve this problem.")
                # if c*z*t**m == Dp for p in k<t> and q = p/(z*t**m) in k[t] and
                # deg(q) <= n:
                #     return q
                # else:
                #     raise NonElementaryIntegralException

    if c.is_zero:
        return c  # return 0

    if n < c.degree(DE.t):
        raise NonElementaryIntegralException

    q = Poly(0, DE.t)
    while not c.is_zero:
        m = c.degree(DE.t)
        if n < m:
            raise NonElementaryIntegralException
        # a1 = b + m*Dt/t
        a1 = b.as_expr()
        with DecrementLevel(DE):
            # TODO: Write a dummy function that does this idiom
            a1a, a1d = frac_in(a1, DE.t)
            a1a = a1a*etad + etaa*a1d*Poly(m, DE.t)
            a1d = a1d*etad

            a2a, a2d = frac_in(c.LC(), DE.t)

            sa, sd = rischDE(a1a, a1d, a2a, a2d, DE)
        stm = Poly(sa.as_expr()/sd.as_expr()*DE.t**m, DE.t, expand=False)
        q += stm
        n = m - 1
        c -= b*stm + derivation(stm, DE)  # deg(c) becomes smaller
    return q
Esempio n. 3
0
    nb = order_at(ba, p, DE.t) - order_at(bd, p, DE.t)
    nc = order_at(ca, p, DE.t) - order_at(cd, p, DE.t)

    n = min(0, nc - min(0, nb))
    if not nb:
        # Possible cancellation.

        if case == 'exp':
            dcoeff = DE.d.quo(Poly(DE.t, DE.t))
            with DecrementLevel(DE):  # We are guaranteed to not have problems,
                # because case != 'base'.
                alphaa, alphad = frac_in(-ba.eval(0) / bd.eval(0) / a.eval(0),
                                         DE.t)
                etaa, etad = frac_in(dcoeff, DE.t)
                A = parametric_log_deriv(alphaa, alphad, etaa, etad, DE)
                if A is not None:
                    a, m, z = A
                    if a == 1:
                        n = min(n, m)

        elif case == 'tan':
            dcoeff = DE.d.quo(Poly(DE.t**2 + 1, DE.t))
            with DecrementLevel(DE):  # We are guaranteed to not have problems,
                # because case != 'base'.
                alphaa, alphad = frac_in(
                    im(-ba.eval(sqrt(-1)) / bd.eval(sqrt(-1)) /
                       a.eval(sqrt(-1))), DE.t)
                betaa, betad = frac_in(
                    re(-ba.eval(sqrt(-1)) / bd.eval(sqrt(-1)) /
                       a.eval(sqrt(-1))), DE.t)
Esempio n. 4
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def bound_degree(a, b, cQ, DE, case='auto', parametric=False):
    """
    Bound on polynomial solutions.

    Given a derivation D on k[t] and a, b, c in k[t] with a != 0, return
    n in ZZ such that deg(q) <= n for any solution q in k[t] of
    a*Dq + b*q == c, when parametric=False, or deg(q) <= n for any solution
    c1, ..., cm in Const(k) and q in k[t] of a*Dq + b*q == Sum(ci*gi, (i, 1, m))
    when parametric=True.

    For parametric=False, cQ is c, a Poly; for parametric=True, cQ is Q ==
    [q1, ..., qm], a list of Polys.

    This constitutes step 3 of the outline given in the rde.py docstring.
    """
    from sympy.integrals.prde import (parametric_log_deriv, limited_integrate,
        is_log_deriv_k_t_radical_in_field)
    # TODO: finish writing this and write tests

    if case == 'auto':
        case = DE.case

    da = a.degree(DE.t)
    db = b.degree(DE.t)

    # The parametric and regular cases are identical, except for this part
    if parametric:
        dc = max([i.degree(DE.t) for i in cQ])
    else:
        dc = cQ.degree(DE.t)

    alpha = cancel(-b.as_poly(DE.t).LC().as_expr()/
        a.as_poly(DE.t).LC().as_expr())

    if case == 'base':
        n = max(0, dc - max(db, da - 1))
        if db == da - 1 and alpha.is_Integer:
            n = max(0, alpha, dc - db)

    elif case == 'primitive':
        if db > da:
            n = max(0, dc - db)
        else:
            n = max(0, dc - da + 1)

        etaa, etad = frac_in(DE.d, DE.T[DE.level - 1])

        t1 = DE.t
        with DecrementLevel(DE):
            alphaa, alphad = frac_in(alpha, DE.t)
            if db == da - 1:
                # if alpha == m*Dt + Dz for z in k and m in ZZ:
                try:
                    (za, zd), m = limited_integrate(alphaa, alphad, [(etaa, etad)],
                        DE)
                except NonElementaryIntegralException:
                    pass
                else:
                    assert len(m) == 1
                    n = max(n, m[0])

            elif db == da:
                # if alpha == Dz/z for z in k*:
                    # beta = -lc(a*Dz + b*z)/(z*lc(a))
                    # if beta == m*Dt + Dw for w in k and m in ZZ:
                        # n = max(n, m)
                A = is_log_deriv_k_t_radical_in_field(alphaa, alphad, DE)
                if A is not None:
                    aa, z = A
                    if aa == 1:
                        beta = -(a*derivation(z, DE).as_poly(t1) +
                            b*z.as_poly(t1)).LC()/(z.as_expr()*a.LC())
                        betaa, betad = frac_in(beta, DE.t)
                        try:
                            (za, zd), m = limited_integrate(betaa, betad,
                                [(etaa, etad)], DE)
                        except NonElementaryIntegralException:
                            pass
                        else:
                            assert len(m) == 1
                            n = max(n, m[0])

    elif case == 'exp':
        n = max(0, dc - max(db, da))
        if da == db:
            etaa, etad = frac_in(DE.d.quo(Poly(DE.t, DE.t)), DE.T[DE.level - 1])
            with DecrementLevel(DE):
                alphaa, alphad = frac_in(alpha, DE.t)
                A = parametric_log_deriv(alphaa, alphad, etaa, etad, DE)
                if A is not None:
                    # if alpha == m*Dt/t + Dz/z for z in k* and m in ZZ:
                        # n = max(n, m)
                    a, m, z = A
                    if a == 1:
                        n = max(n, m)

    elif case in ['tan', 'other_nonlinear']:
        delta = DE.d.degree(DE.t)
        lam = DE.d.LC()
        alpha = cancel(alpha/lam)
        n = max(0, dc - max(da + delta - 1, db))
        if db == da + delta - 1 and alpha.is_Integer:
            n = max(0, alpha, dc - db)

    else:
        raise ValueError("case must be one of {'exp', 'tan', 'primitive', "
            "'other_nonlinear', 'base'}, not %s." % case)

    return n
Esempio n. 5
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def special_denom(a, ba, bd, ca, cd, DE, case='auto'):
    """
    Special part of the denominator.

    case is one of {'exp', 'tan', 'primitive'} for the hyperexponential,
    hypertangent, and primitive cases, respectively.  For the
    hyperexponential (resp. hypertangent) case, given a derivation D on
    k[t] and a in k[t], b, c, in k<t> with Dt/t in k (resp. Dt/(t**2 + 1) in
    k, sqrt(-1) not in k), a != 0, and gcd(a, t) == 1 (resp.
    gcd(a, t**2 + 1) == 1), return the quadruplet (A, B, C, 1/h) such that
    A, B, C, h in k[t] and for any solution q in k<t> of a*Dq + b*q == c,
    r = qh in k[t] satisfies A*Dr + B*r == C.

    For case == 'primitive', k<t> == k[t], so it returns (a, b, c, 1) in
    this case.

    This constitutes step 2 of the outline given in the rde.py docstring.
    """
    from sympy.integrals.prde import parametric_log_deriv
    # TODO: finish writing this and write tests

    if case == 'auto':
        case = DE.case

    if case == 'exp':
        p = Poly(DE.t, DE.t)
    elif case == 'tan':
        p = Poly(DE.t**2 + 1, DE.t)
    elif case in ['primitive', 'base']:
        B = ba.to_field().quo(bd)
        C = ca.to_field().quo(cd)
        return (a, B, C, Poly(1, DE.t))
    else:
        raise ValueError("case must be one of {'exp', 'tan', 'primitive', "
            "'base'}, not %s." % case)
    # assert a.div(p)[1]

    nb = order_at(ba, p, DE.t) - order_at(bd, p, DE.t)
    nc = order_at(ca, p, DE.t) - order_at(cd, p, DE.t)

    n = min(0, nc - min(0, nb))
    if not nb:
        # Possible cancellation.

        if case == 'exp':
            dcoeff = DE.d.quo(Poly(DE.t, DE.t))
            with DecrementLevel(DE):  # We are guaranteed to not have problems,
                                      # because case != 'base'.
                alphaa, alphad = frac_in(-ba.eval(0)/bd.eval(0)/a.eval(0), DE.t)
                etaa, etad = frac_in(dcoeff, DE.t)
                A = parametric_log_deriv(alphaa, alphad, etaa, etad, DE)
                if A is not None:
                    a, m, z = A
                    if a == 1:
                        n = min(n, m)
        else:
            raise NotImplementedError("Tangent case not implemented yet for "
                "RDE special_denom().")
        #     if alpha == m*Dt/t + Dz/z # parametric logarithmic derivative problem
        #         n = min(n, m)
        # elif case == 'tan':
        #     alpha*sqrt(-1) + beta = (-b/a).rem(p) == -b(sqrt(-1))/a(sqrt(-1))
        #     eta = derivation(t, DE).quo(Poly(t**2 + 1, t)) # eta in k
        #     if 2*beta == Dv/v for some v in k* (see pg. 176) and \
        #     alpha*sqrt(-1) + beta == 2*m*eta*sqrt(-1) + Dz/z:
        #     # parametric logarithmic derivative problem
        #         n = min(n, m)

    N = max(0, -nb, n - nc)
    pN = p**N
    pn = p**-n

    A = a*pN
    B = ba*pN.quo(bd) + Poly(n, DE.t)*a*derivation(p, DE).quo(p)*pN
    C = (ca*pN*pn).quo(cd)
    h = pn

    # (a*p**N, (b + n*a*Dp/p)*p**N, c*p**(N - n), p**-n)
    return (A, B, C, h)
Esempio n. 6
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File: rde.py Progetto: vchekan/sympy
    # assert a.div(p)[1]

    nb = order_at(ba, p, DE.t) - order_at(bd, p, DE.t)
    nc = order_at(ca, p, DE.t) - order_at(cd, p, DE.t)

    n = min(0, nc - min(0, nb))
    if not nb:
        # Possible cancellation.

        if case == 'exp':
            dcoeff = DE.d.quo(Poly(DE.t, DE.t))
            with DecrementLevel(DE):  # We are guaranteed to not have problems,
                                      # because case != 'base'.
                alphaa, alphad = frac_in(-ba.eval(0)/bd.eval(0)/a.eval(0), DE.t)
                etaa, etad = frac_in(dcoeff, DE.t)
                A = parametric_log_deriv(alphaa, alphad, etaa, etad, DE)
                if A is not None:
                    a, m, z = A
                    if a == 1:
                        n = min(n, m)
        else:
            raise NotImplementedError("Tangent case not implemented yet for "
                "RDE special_denom().")
        #     if alpha == m*Dt/t + Dz/z # parametric logarithmic derivative problem
        #         n = min(n, m)
        # elif case == 'tan':
        #     alpha*sqrt(-1) + beta = (-b/a).rem(p) == -b(sqrt(-1))/a(sqrt(-1))
        #     eta = derivation(t, DE).quo(Poly(t**2 + 1, t)) # eta in k
        #     if 2*beta == Dv/v for some v in k* (see pg. 176) and \
        #     alpha*sqrt(-1) + beta == 2*m*eta*sqrt(-1) + Dz/z:
        #     # parametric logarithmic derivative problem
Esempio n. 7
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    nb = order_at(ba, p, DE.t) - order_at(bd, p, DE.t)
    nc = order_at(ca, p, DE.t) - order_at(cd, p, DE.t)

    n = min(0, nc - min(0, nb))
    if not nb:
        # Possible cancellation.

        if case == 'exp':
            dcoeff = DE.d.quo(Poly(DE.t, DE.t))
            with DecrementLevel(DE):  # We are guaranteed to not have problems,
                # because case != 'base'.
                alphaa, alphad = frac_in(-ba.eval(0) / bd.eval(0) / a.eval(0),
                                         DE.t)
                etaa, etad = frac_in(dcoeff, DE.t)
                A = parametric_log_deriv(alphaa, alphad, etaa, etad, DE)
                if A is not None:
                    Q, m, z = A
                    if Q == 1:
                        n = min(n, m)

        elif case == 'tan':
            dcoeff = DE.d.quo(Poly(DE.t**2 + 1, DE.t))
            with DecrementLevel(DE):  # We are guaranteed to not have problems,
                # because case != 'base'.
                alphaa, alphad = frac_in(
                    im(-ba.eval(sqrt(-1)) / bd.eval(sqrt(-1)) /
                       a.eval(sqrt(-1))), DE.t)
                betaa, betad = frac_in(
                    re(-ba.eval(sqrt(-1)) / bd.eval(sqrt(-1)) /
                       a.eval(sqrt(-1))), DE.t)