test_sums_products.py 文件源码

def test_hypersum():
    from sympy import sin
    assert simplify(summation(x**n/fac(n), (n, 1, oo))) == -1 + exp(x)
    assert summation((-1)**n * x**(2*n) / fac(2*n), (n, 0, oo)) == cos(x)
    assert simplify(summation((-1)**n*x**(2*n + 1) /
        factorial(2*n + 1), (n, 3, oo))) == -x + sin(x) + x**3/6 - x**5/120

    assert summation(1/(n + 2)**3, (n, 1, oo)) == -S(9)/8 + zeta(3)
    assert summation(1/n**4, (n, 1, oo)) == pi**4/90

    s = summation(x**n*n, (n, -oo, 0))
    assert s.is_Piecewise
    assert s.args[0].args[0] == -1/(x*(1 - 1/x)**2)
    assert s.args[0].args[1] == (abs(1/x) < 1)

    m = Symbol('n', integer=True, positive=True)
    assert summation(binomial(m, k), (k, 0, m)) == 2**m