def eval(cls, arg):
if arg.is_Number:
if arg is S.NaN:
return S.NaN
elif arg is S.Infinity:
return S.Infinity
elif arg.is_Integer:
if arg.is_positive:
return C.Factorial(arg - 1)
else:
return S.ComplexInfinity
elif arg.is_Rational:
if arg.q == 2:
n = abs(arg.p) // arg.q
if arg.is_positive:
k, coeff = n, S.One
else:
n = k = n + 1
if n & 1 == 0:
coeff = S.One
else:
coeff = S.NegativeOne
for i in range(3, 2 * k, 2):
coeff *= i
if arg.is_positive:
return coeff * sqrt(S.Pi) / 2**n
else:
return 2**n * sqrt(S.Pi) / coeff
def _eval_expand_func(self, deep=True, **hints):
if deep:
hints['func'] = False
n = self.args[0].expand(deep, **hints)
z = self.args[1].expand(deep, **hints)
else:
n, z = self.args[0], self.args[1].expand(deep, func=True)
if n.is_Integer and n.is_nonnegative:
if z.is_Add:
coeff, factors = z.as_coeff_factors()
if coeff.is_Integer:
tail = Add(*[z + i for i in xrange(0, int(coeff))])
return polygamma(
n, z - coeff) + (-1)**n * C.Factorial(n) * tail
elif z.is_Mul:
coeff, terms = z.as_coeff_terms()
if coeff.is_Integer and coeff.is_positive:
tail = [
polygamma(n, z + i // coeff)
for i in xrange(0, int(coeff))
]
if n is S.Zero:
return log(coeff) + Add(*tail) / coeff**(n + 1)
else:
return Add(*tail) / coeff**(n + 1)
return polygamma(n, z)
def _eval_expand_func(self, deep=True, **hints):
if deep:
hints['func'] = False
n = self.args[0].expand(deep, **hints)
z = self.args[1].expand(deep, **hints)
else:
n, z = self.args[0], self.args[1].expand(deep, func=True)
if n.is_Integer and n.is_nonnegative:
if z.is_Add:
coeff = z.args[0]
if coeff.is_Integer:
e = -(n + 1)
if coeff > 0:
tail = Add(*[C.Pow(z - i, e) for i in xrange(1, int(coeff) + 1)])
else:
tail = -Add(*[C.Pow(z + i, e) for i in xrange(0, int(-coeff))])
return polygamma(n, z - coeff) + (-1)**n*C.Factorial(n)*tail
elif z.is_Mul:
coeff, z = z.as_two_terms()
if coeff.is_Integer and coeff.is_positive:
tail = [ polygamma(n, z + C.Rational(i, coeff)) for i in xrange(0, int(coeff)) ]
if n == 0:
return Add(*tail)/coeff + log(coeff)
else:
return Add(*tail)/coeff**(n+1)
return polygamma(n, z)
def eval(cls, n, z):
n, z = map(sympify, (n, z))
if n.is_integer:
if n.is_negative:
return loggamma(z)
else:
if z.is_Number:
if z is S.NaN:
return S.NaN
elif z is S.Infinity:
if n.is_Number:
if n is S.Zero:
return S.Infinity
else:
return S.Zero
elif z.is_Integer:
if z.is_nonpositive:
return S.ComplexInfinity
else:
if n is S.Zero:
return -S.EulerGamma + C.harmonic(z - 1, 1)
elif n.is_odd:
return (-1)**(n + 1) * C.Factorial(n) * zeta(
n + 1, z)
def eval(cls, z, a=S.One):
z, a = map(sympify, (z, a))
if a.is_Number:
if a is S.NaN:
return S.NaN
elif a is S.Zero:
return cls(z)
if z.is_Number:
if z is S.NaN:
return S.NaN
elif z is S.Infinity:
return S.One
elif z is S.Zero:
if a.is_negative:
return S.Half - a - 1
else:
return S.Half - a
elif z is S.One:
return S.ComplexInfinity
elif z.is_Integer:
if a.is_Integer:
if z.is_negative:
zeta = (-1)**z * C.bernoulli(-z+1)/(-z+1)
elif z.is_even:
B, F = C.bernoulli(z), C.Factorial(z)
zeta = 2**(z-1) * abs(B) * pi**z / F
else:
return
if a.is_negative:
return zeta + C.harmonic(abs(a), z)
else:
return zeta - C.harmonic(a-1, z)
def taylor_term(n, x, *previous_terms):
if n < 0: return S.Zero
if n == 0: return S.One
x = sympify(x)
if previous_terms:
p = previous_terms[-1]
if p is not None:
return p * x / n
return x**n / C.Factorial()(n)
def taylor_term(n, x, *previous_terms):
if n < 0 or n % 2 == 0:
return S.Zero
else:
x = sympify(x)
if len(previous_terms) > 2:
p = previous_terms[-2]
return p * x**2 / (n*(n-1))
else:
return x**(n) / C.Factorial(n)
def taylor_term(n, x, *previous_terms):
if n < 0 or n % 2 == 0:
return S.Zero
else:
x = sympify(x)
k = (n - 1) // 2
if len(previous_terms) > 2:
return -previous_terms[-2] * x**2 * (n - 2) / (n * k)
else:
return 2 * (-1)**k * x**n / (n * C.Factorial(k) * sqrt(S.Pi))
def taylor_term(n, x, *previous_terms):
if n == 0:
return 1 / sympify(x)
elif n < 0 or n % 2 == 0:
return S.Zero
else:
x = sympify(x)
B = C.bernoulli(n+1)
F = C.Factorial(n+1)
return 2**(n+1) * B/F * x**n
def taylor_term(n, x, *previous_terms):
if n < 0 or n % 2 == 0:
return S.Zero
else:
x = sympify(x)
if len(previous_terms) >= 2 and n > 2:
p = previous_terms[-2]
return -p * (n-2)**2/(n*(n-1)) * x**2
else:
k = (n - 1) // 2
R = C.RisingFactorial(S.Half, k)
F = C.Factorial(k)
return (-1)**k * R / F * x**n / n
def _eval_rewrite_as_zeta(self, n, z):
return (-1)**(n + 1) * C.Factorial(n) * zeta(n + 1, z - 1)
def euler_maclaurin(self, m=0, n=0, eps=0, eval_integral=True):
"""
Return an Euler-Maclaurin approximation of self, where m is the
number of leading terms to sum directly and n is the number of
terms in the tail.
With m = n = 0, this is simply the corresponding integral
plus a first-order endpoint correction.
Returns (s, e) where s is the Euler-Maclaurin approximation
and e is the estimated error (taken to be the magnitude of
the first omitted term in the tail):
>>> k = Symbol('k')
>>> Sum(1/k, (k, 2, 5)).doit().evalf()
1.28333333333333
>>> s, e = Sum(1/k, (k, 2, 5)).euler_maclaurin()
>>> s
7/20 - log(2) + log(5)
>>> from sympy import sstr
>>> print sstr((s.evalf(), e.evalf()), full_prec=True)
(1.26629073187416, 0.0175000000000000)
The endpoints may be symbolic:
>>> k, a, b = symbols('kab')
>>> s, e = Sum(1/k, (k, a, b)).euler_maclaurin()
>>> s
-log(a) + log(b) + 1/(2*a) + 1/(2*b)
>>> e
abs(-1/(12*b**2) + 1/(12*a**2))
If the function is a polynomial of degree at most 2n+1, the
Euler-Maclaurin formula becomes exact (and e = 0 is returned):
>>> Sum(k, (k, 2, b)).euler_maclaurin()
(-1 + b/2 + b**2/2, 0)
>>> Sum(k, (k, 2, b)).doit()
-1 + b/2 + b**2/2
With a nonzero eps specified, the summation is ended
as soon as the remainder term is less than the epsilon.
"""
m = int(m)
n = int(n)
f = self.function
assert len(self.limits) == 1
i, a, b = self.limits[0]
s = S.Zero
if m:
for k in range(m):
term = f.subs(i, a + k)
if (eps and term and abs(term.evalf(3)) < eps):
return s, abs(term)
s += term
a += m
x = Symbol('x', dummy=True)
I = C.Integral(f.subs(i, x), (x, a, b))
if eval_integral:
I = I.doit()
s += I
def fpoint(expr):
if b is S.Infinity:
return expr.subs(i, a), 0
return expr.subs(i, a), expr.subs(i, b)
fa, fb = fpoint(f)
iterm = (fa + fb) / 2
g = f.diff(i)
for k in xrange(1, n + 2):
ga, gb = fpoint(g)
term = C.bernoulli(2 * k) / C.Factorial(2 * k) * (gb - ga)
if (eps and term and abs(term.evalf(3)) < eps) or (k > n):
break
s += term
g = g.diff(i, 2)
return s + iterm, abs(term)
