Python limits.limit函数代码示例

 def _dirichlet_test(g_n):
     try:
         ing_val = limit(Sum(g_n, (sym, interval.inf, m)).doit(), m, S.Infinity)
         if ing_val.is_finite:
             return S.true
     except NotImplementedError:
         pass

def test_limit2():
    assert limit(x**x, x, 0, dir="+") == 1
    assert limit((exp(x)-1)/x, x, 0) == 1
    assert limit(1+1/x,x,oo) == 1
    assert limit(-exp(1/x),x,oo) == -1
    assert limit(x+exp(-x),x,oo) == oo
    assert limit(x+exp(-x**2),x,oo) == oo
    assert limit(x+exp(-exp(x)),x,oo) == oo
    assert limit(13+1/x-exp(-x),x,oo) == 13

def test_limits():
    k, x = symbols('k, x')
    assert hyper((1,), (S(4)/3, S(5)/3), k**2).series(k) == \
           hyper((1,), (S(4)/3, S(5)/3), 0) + \
           9*k**2*hyper((2,), (S(7)/3, S(8)/3), 0)/20 + \
           81*k**4*hyper((3,), (S(10)/3, S(11)/3), 0)/1120 + \
           O(k**6) # issue 6350
    assert limit(meijerg((), (), (1,), (0,), -x), x, 0) == \
            meijerg(((), ()), ((1,), (0,)), 0) # issue 6052

 def _bounded_convergent_test(g1_n, g2_n):
     try:
         lim_val = limit(g1_n, sym, upper_limit)
         if lim_val.is_finite or (isinstance(lim_val, AccumulationBounds)
                                  and (lim_val.max - lim_val.min).is_finite):
             if Sum(g2_n, (sym, lower_limit, upper_limit)).is_absolutely_convergent():
                 return S.true
     except NotImplementedError:
         pass

    def is_convergent(self):
        r"""Checks for the convergence of a Sum.

        We divide the study of convergence of infinite sums and products in
        two parts.

        First Part:
        One part is the question whether all the terms are well defined, i.e.,
        they are finite in a sum and also non-zero in a product. Zero
        is the analogy of (minus) infinity in products as
        :math:`e^{-\infty} = 0`.

        Second Part:
        The second part is the question of convergence after infinities,
        and zeros in products, have been omitted assuming that their number
        is finite. This means that we only consider the tail of the sum or
        product, starting from some point after which all terms are well
        defined.

        For example, in a sum of the form:

        .. math::

            \sum_{1 \leq i < \infty} \frac{1}{n^2 + an + b}

        where a and b are numbers. The routine will return true, even if there
        are infinities in the term sequence (at most two). An analogous
        product would be:

        .. math::

            \prod_{1 \leq i < \infty} e^{\frac{1}{n^2 + an + b}}

        This is how convergence is interpreted. It is concerned with what
        happens at the limit. Finding the bad terms is another independent
        matter.

        Note: It is responsibility of user to see that the sum or product
        is well defined.

        There are various tests employed to check the convergence like
        divergence test, root test, integral test, alternating series test,
        comparison tests, Dirichlet tests. It returns true if Sum is convergent
        and false if divergent and NotImplementedError if it can not be checked.

        References
        ==========

        .. [1] https://en.wikipedia.org/wiki/Convergence_tests

        Examples
        ========

        >>> from sympy import factorial, S, Sum, Symbol, oo
        >>> n = Symbol('n', integer=True)
        >>> Sum(n/(n - 1), (n, 4, 7)).is_convergent()
        True
        >>> Sum(n/(2*n + 1), (n, 1, oo)).is_convergent()
        False
        >>> Sum(factorial(n)/5**n, (n, 1, oo)).is_convergent()
        False
        >>> Sum(1/n**(S(6)/5), (n, 1, oo)).is_convergent()
        True

        See Also
        ========

        Sum.is_absolutely_convergent()

        Product.is_convergent()
        """
        from sympy import Interval, Integral, Limit, log, symbols, Ge, Gt, simplify
        p, q = symbols('p q', cls=Wild)

        sym = self.limits[0][0]
        lower_limit = self.limits[0][1]
        upper_limit = self.limits[0][2]
        sequence_term = self.function

        if len(sequence_term.free_symbols) > 1:
            raise NotImplementedError("convergence checking for more than one symbol "
                                      "containing series is not handled")

        if lower_limit.is_finite and upper_limit.is_finite:
            return S.true

        # transform sym -> -sym and swap the upper_limit = S.Infinity
        # and lower_limit = - upper_limit
        if lower_limit is S.NegativeInfinity:
            if upper_limit is S.Infinity:
                return Sum(sequence_term, (sym, 0, S.Infinity)).is_convergent() and \
                        Sum(sequence_term, (sym, S.NegativeInfinity, 0)).is_convergent()
            sequence_term = simplify(sequence_term.xreplace({sym: -sym}))
            lower_limit = -upper_limit
            upper_limit = S.Infinity

        sym_ = Dummy(sym.name, integer=True, positive=True)
        sequence_term = sequence_term.xreplace({sym: sym_})
        sym = sym_

#.........这里部分代码省略.........

 def limit(self, x, xlim, dir='+'):
     """ Compute limit x->xlim.
     """
     from sympy.series.limits import limit
     return TupleArg(*[limit(f, x, xlim, dir) for f in self.args])

def test_limit4():
    #issue 364
    assert limit((3**x+5**x)**(1/x), x, oo) == 5
    #issue 364
    assert limit((3**(1/x)+5**(1/x))**x, x, 0) == 5

def test_limit3():
    a = Symbol('a')
    assert limit(x-log(1+exp(x)), x, oo) == 0
    assert limit(x-log(a+exp(x)), x, oo) == 0
    assert limit(exp(x)/(1+exp(x)), x, oo) == 1
    assert limit(exp(x)/(a+exp(x)), x, oo) == 1

def test_limit1():
    assert limit(x, x, oo) == oo
    assert limit(x, x, -oo) == -oo
    assert limit(-x, x, oo) == -oo
    assert limit(x**2, x, -oo) == oo
    assert limit(-x**2, x, oo) == -oo
    assert limit(x*log(x), x, 0, dir="+") == 0
    assert limit(1/x,x,oo) == 0
    assert limit(exp(x),x,oo) == oo
    assert limit(-exp(x),x,oo) == -oo
    assert limit(exp(x)/x,x,oo) == oo
    assert limit(1/x-exp(-x),x,oo) == 0
    assert limit(x+1/x,x,oo) == oo

def _limit_inf(expr, n):
    try:
        return limit(expr, n, S.Infinity)
    except (NotImplementedError, PoleError):
        return None

    def is_convergent(self):
        """
        Convergence tests are used for checking the convergence of
        a series. There are various tests employed to check the convergence,
        returns true if convergent and false if divergent and NotImplementedError
        if can not be checked. Like divergence test, root test, integral test,
        alternating series test, comparison tests, Dirichlet tests.

        References
        ==========

        .. [1] https://en.wikipedia.org/wiki/Convergence_tests

        Examples
        ========

        >>> from sympy import Interval, factorial, S, Sum, Symbol, oo
        >>> n = Symbol('n', integer=True)
        >>> Sum(n/(n - 1), (n, 4, 7)).is_convergent()
        True
        >>> Sum(n/(2*n + 1), (n, 1, oo)).is_convergent()
        False
        >>> Sum(factorial(n)/5**n, (n, 1, oo)).is_convergent()
        False
        >>> Sum(1/n**(S(6)/5), (n, 1, oo)).is_convergent()
        True

        See Also
        ========

        Sum.is_absolute_convergent()
        """
        from sympy import Interval, Integral, Limit, log, symbols, Ge, Gt, simplify
        p, q = symbols('p q', cls=Wild)

        sym = self.limits[0][0]
        lower_limit = self.limits[0][1]
        upper_limit = self.limits[0][2]
        sequence_term = self.function

        if len(sequence_term.free_symbols) > 1:
            raise NotImplementedError("convergence checking for more that one symbol \
                                        containing series is not handled")

        if lower_limit.is_finite and upper_limit.is_finite:
            return S.true

        # transform sym -> -sym and swap the upper_limit = S.Infinity and lower_limit = - upper_limit
        if lower_limit is S.NegativeInfinity:
            if upper_limit is S.Infinity:
                return Sum(sequence_term, (sym, 0, S.Infinity)).is_convergent() and \
                        Sum(sequence_term, (sym, S.NegativeInfinity, 0)).is_convergent()
            sequence_term = simplify(sequence_term.xreplace({sym: -sym}))
            lower_limit = -upper_limit
            upper_limit = S.Infinity

        interval = Interval(lower_limit, upper_limit)

        # Piecewise function handle
        if sequence_term.is_Piecewise:
            for func_cond in sequence_term.args:
                if func_cond[1].func is Ge or func_cond[1].func is Gt or func_cond[1] == True:
                    return Sum(func_cond[0], (sym, lower_limit, upper_limit)).is_convergent()
            return S.true

        ###  -------- Divergence test ----------- ###
        try:
            lim_val = limit(abs(sequence_term), sym, upper_limit)
            if lim_val.is_number and lim_val != S.Zero:
                return S.false
        except NotImplementedError:
            pass

        order = O(sequence_term, (sym, S.Infinity))

        ### --------- p-series test (1/n**p) ---------- ###
        p1_series_test = order.expr.match(sym**p)
        if p1_series_test is not None:
            if p1_series_test[p] < -1:
                return S.true
            if p1_series_test[p] > -1:
                return S.false

        p2_series_test = order.expr.match((1/sym)**p)
        if p2_series_test is not None:
            if p2_series_test[p] > 1:
                return S.true
            if p2_series_test[p] < 1:
                return S.false

        ### ----------- root test ---------------- ###
        lim = Limit(abs(sequence_term)**(1/sym), sym, S.Infinity)
        lim_evaluated = lim.doit()
        if lim_evaluated.is_number:
            if lim_evaluated < 1:
                return S.true
            if lim_evaluated > 1:
                return S.false

        ### ------------- alternating series test ----------- ###
#.........这里部分代码省略.........