def _eval_(self, x):
"""
EXAMPLES::
sage: airy_bi_prime(0)
3^(1/6)/gamma(1/3)
sage: airy_bi_prime(0.0)
0.448288357353826
"""
if x == 0:
one_sixth = ZZ(1) / 6
return 3 ** (one_sixth) / gamma(2 * one_sixth)
def _eval_(self, x):
"""
EXAMPLES::
sage: airy_ai_prime(0)
-1/3*3^(2/3)/gamma(1/3)
sage: airy_ai_prime(0.0)
-0.258819403792807
"""
if x == 0:
r = ZZ(1) / 3
return -1 / (3 ** (r) * gamma(r))
def _derivative_(self, a, z, diff_param=None):
"""
EXAMPLES::
sage: diff(struve_L(1,x),x)
1/3*x/pi - 1/2*struve_L(2, x) + 1/2*struve_L(0, x)
"""
if diff_param == 0:
raise ValueError("cannot differentiate struve_L in the first parameter")
from sage.functions.other import sqrt, gamma
return (z**a/(sqrt(pi)*2**a*gamma(a+Integer(3)/Integer(2)))-struve_L(a+1,z)+struve_L(a-1,z))/2
def _derivative_(self, a, z, diff_param=None):
"""
EXAMPLES::
sage: diff(struve_H(3/2,x),x)
-1/2*sqrt(2)*sqrt(1/(pi*x))*(cos(x) - 1) + 1/16*sqrt(2)*x^(3/2)/sqrt(pi) - 1/2*struve_H(5/2, x)
"""
if diff_param == 0:
raise ValueError("cannot differentiate struve_H in the first parameter")
from sage.functions.other import sqrt, gamma
return (z**a/(sqrt(pi)*2**a*gamma(a+Integer(3)/Integer(2)))-struve_H(a+1,z)+struve_H(a-1,z))/2
def inverse_gamma_derivative(shift, r):
"""
Return value of `r`-th derivative of 1/Gamma
at alpha-shift.
"""
if r == 0:
result = iga*falling_factorial(alpha-1, shift)
else:
result = limit((1/gamma(s)).diff(s, r), s=alpha-shift)
try:
return coefficient_ring(result)
except TypeError:
return result
def inverse_gamma_derivative(shift, r):
"""
Return value of `r`-th derivative of 1/Gamma
at alpha-shift.
"""
if r == 0:
result = iga * falling_factorial(alpha - 1, shift)
else:
result = limit((1 / gamma(s)).diff(s, r), s=alpha - shift)
try:
return coefficient_ring(result)
except TypeError:
return result
def _eval_(self, x):
"""
EXAMPLES::
sage: from sage.functions.airy import airy_ai_simple
sage: airy_ai_simple(0)
1/3*3^(1/3)/gamma(2/3)
sage: airy_ai_simple(0.0)
0.355028053887817
sage: airy_ai_simple(I)
airy_ai(I)
sage: airy_ai_simple(1.0 * I)
0.331493305432141 - 0.317449858968444*I
"""
if x == 0:
r = ZZ(2) / 3
return 1 / (3 ** (r) * gamma(r))
def _eval_(self, x):
"""
EXAMPLES::
sage: from sage.functions.airy import airy_bi_simple
sage: airy_bi_simple(0)
1/3*3^(5/6)/gamma(2/3)
sage: airy_bi_simple(0.0)
0.614926627446001
sage: airy_bi_simple(0).n() == airy_bi(0.0)
True
sage: airy_bi_simple(I)
airy_bi(I)
sage: airy_bi_simple(1.0 * I)
0.648858208330395 + 0.344958634768048*I
"""
if x == 0:
one_sixth = ZZ(1) / 6
return 1 / (3 ** (one_sixth) * gamma(4 * one_sixth))
def SingularityAnalysis(var, zeta=1, alpha=0, beta=0, delta=0,
precision=None, normalized=True):
r"""
Return the asymptotic expansion of the coefficients of
an power series with specified pole and logarithmic singularity.
More precisely, this extracts the `n`-th coefficient
.. MATH::
[z^n] \left(\frac{1}{1-z/\zeta}\right)^\alpha
\left(\frac{1}{z/\zeta} \log \frac{1}{1-z/\zeta}\right)^\beta
\left(\frac{1}{z/\zeta} \log
\left(\frac{1}{z/\zeta} \log \frac{1}{1-z/\zeta}\right)\right)^\delta
(if ``normalized=True``, the default) or
.. MATH::
[z^n] \left(\frac{1}{1-z/\zeta}\right)^\alpha
\left(\log \frac{1}{1-z/\zeta}\right)^\beta
\left(\log
\left(\frac{1}{z/\zeta} \log \frac{1}{1-z/\zeta}\right)\right)^\delta
(if ``normalized=False``).
INPUT:
- ``var`` -- a string for the variable name.
- ``zeta`` -- (default: `1`) the location of the singularity.
- ``alpha`` -- (default: `0`) the pole order of the singularty.
- ``beta`` -- (default: `0`) the order of the logarithmic singularity.
- ``delta`` -- (default: `0`) the order of the log-log singularity.
Not yet implemented for ``delta != 0``.
- ``precision`` -- (default: ``None``) an integer. If ``None``, then
the default precision of the asymptotic ring is used.
- ``normalized`` -- (default: ``True``) a boolean, see above.
OUTPUT:
An asymptotic expansion.
EXAMPLES::
sage: asymptotic_expansions.SingularityAnalysis('n', alpha=1)
1
sage: asymptotic_expansions.SingularityAnalysis('n', alpha=2)
n + 1
sage: asymptotic_expansions.SingularityAnalysis('n', alpha=3)
1/2*n^2 + 3/2*n + 1
sage: _.parent()
Asymptotic Ring <n^ZZ> over Rational Field
::
sage: asymptotic_expansions.SingularityAnalysis('n', alpha=-3/2,
....: precision=3)
3/4/sqrt(pi)*n^(-5/2)
+ 45/32/sqrt(pi)*n^(-7/2)
+ 1155/512/sqrt(pi)*n^(-9/2)
+ O(n^(-11/2))
sage: asymptotic_expansions.SingularityAnalysis('n', alpha=-1/2,
....: precision=3)
-1/2/sqrt(pi)*n^(-3/2)
- 3/16/sqrt(pi)*n^(-5/2)
- 25/256/sqrt(pi)*n^(-7/2)
+ O(n^(-9/2))
sage: asymptotic_expansions.SingularityAnalysis('n', alpha=1/2,
....: precision=4)
1/sqrt(pi)*n^(-1/2)
- 1/8/sqrt(pi)*n^(-3/2)
+ 1/128/sqrt(pi)*n^(-5/2)
+ 5/1024/sqrt(pi)*n^(-7/2)
+ O(n^(-9/2))
sage: _.parent()
Asymptotic Ring <n^QQ> over Symbolic Constants Subring
::
sage: S = SR.subring(rejecting_variables=('n',))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=S.var('a'),
....: precision=4).map_coefficients(lambda c: c.factor())
1/gamma(a)*n^(a - 1)
+ (1/2*(a - 1)*a/gamma(a))*n^(a - 2)
+ (1/24*(3*a - 1)*(a - 1)*(a - 2)*a/gamma(a))*n^(a - 3)
+ (1/48*(a - 1)^2*(a - 2)*(a - 3)*a^2/gamma(a))*n^(a - 4)
+ O(n^(a - 5))
sage: _.parent()
Asymptotic Ring <n^(Symbolic Subring rejecting the variable n)>
over Symbolic Subring rejecting the variable n
::
sage: ae = asymptotic_expansions.SingularityAnalysis('n',
....: alpha=1/2, beta=1, precision=4); ae
1/sqrt(pi)*n^(-1/2)*log(n) + ((euler_gamma + 2*log(2))/sqrt(pi))*n^(-1/2)
- 5/8/sqrt(pi)*n^(-3/2)*log(n) + (1/8*(3*euler_gamma + 6*log(2) - 8)/sqrt(pi)
- (euler_gamma + 2*log(2) - 2)/sqrt(pi))*n^(-3/2) + O(n^(-5/2)*log(n))
sage: n = ae.parent().gen()
sage: ae.subs(n=n-1).map_coefficients(lambda x: x.canonicalize_radical())
1/sqrt(pi)*n^(-1/2)*log(n)
+ ((euler_gamma + 2*log(2))/sqrt(pi))*n^(-1/2)
- 1/8/sqrt(pi)*n^(-3/2)*log(n)
+ (-1/8*(euler_gamma + 2*log(2))/sqrt(pi))*n^(-3/2)
+ O(n^(-5/2)*log(n))
::
sage: asymptotic_expansions.SingularityAnalysis('n',
....: alpha=1, beta=1/2, precision=4)
log(n)^(1/2) + 1/2*euler_gamma*log(n)^(-1/2)
+ (-1/8*euler_gamma^2 + 1/48*pi^2)*log(n)^(-3/2)
+ (1/16*euler_gamma^3 - 1/32*euler_gamma*pi^2 + 1/8*zeta(3))*log(n)^(-5/2)
+ O(log(n)^(-7/2))
::
sage: ae = asymptotic_expansions.SingularityAnalysis('n',
....: alpha=0, beta=2, precision=14)
sage: n = ae.parent().gen()
sage: ae.subs(n=n-2)
2*n^(-1)*log(n) + 2*euler_gamma*n^(-1) - n^(-2) - 1/6*n^(-3) + O(n^(-5))
::
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=-1/2, beta=1, precision=2, normalized=False)
-1/2/sqrt(pi)*n^(-3/2)*log(n)
+ (-1/2*(euler_gamma + 2*log(2) - 2)/sqrt(pi))*n^(-3/2)
+ O(n^(-5/2)*log(n))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1/2, alpha=0, beta=1, precision=3, normalized=False)
2^n*n^(-1) + O(2^n*n^(-2))
ALGORITHM:
See [FS2009]_ together with the
`errata list <http://algo.inria.fr/flajolet/Publications/AnaCombi/errata.pdf>`_.
REFERENCES:
.. [FS2009] Philippe Flajolet and Robert Sedgewick,
`Analytic combinatorics <http://algo.inria.fr/flajolet/Publications/AnaCombi/book.pdf>`_.
Cambridge University Press, Cambridge, 2009.
TESTS::
sage: ex = asymptotic_expansions.SingularityAnalysis('n', alpha=-1/2,
....: precision=4)
sage: n = ex.parent().gen()
sage: coefficients = ((1-x)^(1/2)).series(
....: x, 21).truncate().coefficients(x, sparse=False)
sage: ex.compare_with_values(n, # rel tol 1e-6
....: lambda k: coefficients[k], [5, 10, 20])
[(5, 0.015778873294?), (10, 0.01498952777?), (20, 0.0146264622?)]
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=3, precision=2)
1/2*n^2 + 3/2*n + O(1)
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=3, precision=3)
1/2*n^2 + 3/2*n + 1
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=3, precision=4)
1/2*n^2 + 3/2*n + 1
::
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=0)
Traceback (most recent call last):
...
NotImplementedOZero: The error term in the result is O(0)
which means 0 for sufficiently large n.
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=-1)
Traceback (most recent call last):
...
NotImplementedOZero: The error term in the result is O(0)
which means 0 for sufficiently large n.
::
sage: asymptotic_expansions.SingularityAnalysis(
....: 'm', alpha=-1/2, precision=3)
-1/2/sqrt(pi)*m^(-3/2)
- 3/16/sqrt(pi)*m^(-5/2)
- 25/256/sqrt(pi)*m^(-7/2)
+ O(m^(-9/2))
sage: _.parent()
Asymptotic Ring <m^QQ> over Symbolic Constants Subring
Location of the singularity::
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=1, zeta=2, precision=3)
(1/2)^n
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=1, zeta=1/2, precision=3)
2^n
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=1, zeta=CyclotomicField(3).gen(),
....: precision=3)
(-zeta3 - 1)^n
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=4, zeta=2, precision=3)
1/6*(1/2)^n*n^3 + (1/2)^n*n^2 + 11/6*(1/2)^n*n + O((1/2)^n)
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=-1, zeta=2, precision=3)
Traceback (most recent call last):
...
NotImplementedOZero: The error term in the result is O(0)
which means 0 for sufficiently large n.
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=1/2, zeta=2, precision=3)
1/sqrt(pi)*(1/2)^n*n^(-1/2) - 1/8/sqrt(pi)*(1/2)^n*n^(-3/2)
+ 1/128/sqrt(pi)*(1/2)^n*n^(-5/2) + O((1/2)^n*n^(-7/2))
The following tests correspond to Table VI.5 in [FS2009]_. ::
sage: A.<n> = AsymptoticRing('n^QQ * log(n)^QQ', QQ)
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=-1/2, beta=1, precision=2,
....: normalized=False) * (- sqrt(pi*n^3))
1/2*log(n) + 1/2*euler_gamma + log(2) - 1 + O(n^(-1)*log(n))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=0, beta=1, precision=3,
....: normalized=False)
n^(-1) + O(n^(-2))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=0, beta=2, precision=14,
....: normalized=False) * n
2*log(n) + 2*euler_gamma - n^(-1) - 1/6*n^(-2) + O(n^(-4))
sage: (asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=1/2, beta=1, precision=4,
....: normalized=False) * sqrt(pi*n)).\
....: map_coefficients(lambda x: x.expand())
log(n) + euler_gamma + 2*log(2) - 1/8*n^(-1)*log(n) +
(-1/8*euler_gamma - 1/4*log(2))*n^(-1) + O(n^(-2)*log(n))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=1, beta=1, precision=13,
....: normalized=False)
log(n) + euler_gamma + 1/2*n^(-1) - 1/12*n^(-2) + 1/120*n^(-4)
+ O(n^(-6))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=1, beta=2, precision=4,
....: normalized=False)
log(n)^2 + 2*euler_gamma*log(n) + euler_gamma^2 - 1/6*pi^2
+ O(n^(-1)*log(n))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=3/2, beta=1, precision=3,
....: normalized=False) * sqrt(pi/n)
2*log(n) + 2*euler_gamma + 4*log(2) - 4 + 3/4*n^(-1)*log(n)
+ O(n^(-1))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=2, beta=1, precision=5,
....: normalized=False)
n*log(n) + (euler_gamma - 1)*n + log(n) + euler_gamma + 1/2
+ O(n^(-1))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=2, beta=2, precision=4,
....: normalized=False) / n
log(n)^2 + (2*euler_gamma - 2)*log(n)
- 2*euler_gamma + euler_gamma^2 - 1/6*pi^2 + 2
+ n^(-1)*log(n)^2 + O(n^(-1)*log(n))
Be aware that the last result does *not* coincide with [FS2009]_,
they do have a different error term.
Checking parameters::
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, 1, 1/2, precision=0, normalized=False)
Traceback (most recent call last):
...
ValueError: beta and delta must be integers
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, 1, 1, 1/2, normalized=False)
Traceback (most recent call last):
...
ValueError: beta and delta must be integers
::
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=0, beta=0, delta=1, precision=3)
Traceback (most recent call last):
...
NotImplementedError: not implemented for delta!=0
"""
from itertools import islice, count
from asymptotic_ring import AsymptoticRing
from growth_group import ExponentialGrowthGroup, \
MonomialGrowthGroup
from sage.arith.all import falling_factorial
from sage.categories.cartesian_product import cartesian_product
from sage.functions.other import binomial, gamma
from sage.calculus.calculus import limit
from sage.misc.cachefunc import cached_function
from sage.arith.srange import srange
from sage.rings.rational_field import QQ
from sage.rings.integer_ring import ZZ
from sage.symbolic.ring import SR
SCR = SR.subring(no_variables=True)
s = SR('s')
iga = 1/gamma(alpha)
if iga.parent() is SR:
try:
iga = SCR(iga)
except TypeError:
pass
coefficient_ring = iga.parent()
if beta != 0:
coefficient_ring = SCR
@cached_function
def inverse_gamma_derivative(shift, r):
"""
Return value of `r`-th derivative of 1/Gamma
at alpha-shift.
"""
if r == 0:
result = iga*falling_factorial(alpha-1, shift)
else:
result = limit((1/gamma(s)).diff(s, r), s=alpha-shift)
try:
return coefficient_ring(result)
except TypeError:
return result
if isinstance(alpha, int):
alpha = ZZ(alpha)
if isinstance(beta, int):
beta = ZZ(beta)
if isinstance(delta, int):
delta = ZZ(delta)
if precision is None:
precision = AsymptoticRing.__default_prec__
if not normalized and not (beta in ZZ and delta in ZZ):
raise ValueError("beta and delta must be integers")
if delta != 0:
raise NotImplementedError("not implemented for delta!=0")
groups = []
if zeta != 1:
groups.append(ExponentialGrowthGroup((1/zeta).parent(), var))
groups.append(MonomialGrowthGroup(alpha.parent(), var))
if beta != 0:
groups.append(MonomialGrowthGroup(beta.parent(), 'log({})'.format(var)))
group = cartesian_product(groups)
A = AsymptoticRing(growth_group=group, coefficient_ring=coefficient_ring,
default_prec=precision)
n = A.gen()
if zeta == 1:
exponential_factor = 1
else:
exponential_factor = n.rpow(1/zeta)
if beta in ZZ and beta >= 0:
it = ((k, r)
for k in count()
for r in srange(beta+1))
k_max = precision
else:
it = ((0, r)
for r in count())
k_max = 0
if beta != 0:
log_n = n.log()
else:
# avoid construction of log(n)
# because it does not exist in growth group.
log_n = 1
it = reversed(list(islice(it, precision+1)))
if normalized:
beta_denominator = beta
else:
beta_denominator = 0
L = _sa_coefficients_lambda_(max(1, k_max), beta=beta_denominator)
(k, r) = next(it)
result = (n**(-k) * log_n**(-r)).O()
if alpha in ZZ and beta == 0:
if alpha > 0 and alpha <= precision:
result = A(0)
elif alpha <= 0 and precision > 0:
from misc import NotImplementedOZero
raise NotImplementedOZero(A)
for (k, r) in it:
result += binomial(beta, r) * \
sum(L[(k, ell)] * (-1)**ell *
inverse_gamma_derivative(ell, r)
for ell in srange(k, 2*k+1)
if (k, ell) in L) * \
n**(-k) * log_n**(-r)
result *= exponential_factor * n**(alpha-1) * log_n**beta
return result
def _closed_form(hyp):
a, b, z = hyp.operands()
a, b = a.operands(), b.operands()
p, q = len(a), len(b)
if z == 0:
return Integer(1)
if p == q == 0:
return exp(z)
if p == 1 and q == 0:
return (1 - z) ** (-a[0])
if p == 0 and q == 1:
# TODO: make this require only linear time
def _0f1(b, z):
F12 = cosh(2 * sqrt(z))
F32 = sinh(2 * sqrt(z)) / (2 * sqrt(z))
if 2 * b == 1:
return F12
if 2 * b == 3:
return F32
if 2 * b > 3:
return ((b - 2) * (b - 1) / z * (_0f1(b - 2, z) -
_0f1(b - 1, z)))
if 2 * b < 1:
return (_0f1(b + 1, z) + z / (b * (b + 1)) *
_0f1(b + 2, z))
raise ValueError
# Can evaluate 0F1 in terms of elementary functions when
# the parameter is a half-integer
if 2 * b[0] in ZZ and b[0] not in ZZ:
return _0f1(b[0], z)
# Confluent hypergeometric function
if p == 1 and q == 1:
aa, bb = a[0], b[0]
if aa * 2 == 1 and bb * 2 == 3:
t = sqrt(-z)
return sqrt(pi) / 2 * erf(t) / t
if a == 1 and b == 2:
return (exp(z) - 1) / z
n, m = aa, bb
if n in ZZ and m in ZZ and m > 0 and n > 0:
rf = rising_factorial
if m <= n:
return (exp(z) * sum(rf(m - n, k) * (-z) ** k /
factorial(k) / rf(m, k) for k in
xrange(n - m + 1)))
else:
T = sum(rf(n - m + 1, k) * z ** k /
(factorial(k) * rf(2 - m, k)) for k in
xrange(m - n))
U = sum(rf(1 - n, k) * (-z) ** k /
(factorial(k) * rf(2 - m, k)) for k in
xrange(n))
return (factorial(m - 2) * rf(1 - m, n) *
z ** (1 - m) / factorial(n - 1) *
(T - exp(z) * U))
if p == 2 and q == 1:
R12 = QQ('1/2')
R32 = QQ('3/2')
def _2f1(a, b, c, z):
"""
Evaluation of 2F1(a, b; c; z), assuming a, b, c positive
integers or half-integers
"""
if b == c:
return (1 - z) ** (-a)
if a == c:
return (1 - z) ** (-b)
if a == 0 or b == 0:
return Integer(1)
if a > b:
a, b = b, a
if b >= 2:
F1 = _2f1(a, b - 1, c, z)
F2 = _2f1(a, b - 2, c, z)
q = (b - 1) * (z - 1)
return (((c - 2 * b + 2 + (b - a - 1) * z) * F1 +
(b - c - 1) * F2) / q)
if c > 2:
# how to handle this case?
if a - c + 1 == 0 or b - c + 1 == 0:
raise NotImplementedError
F1 = _2f1(a, b, c - 1, z)
F2 = _2f1(a, b, c - 2, z)
r1 = (c - 1) * (2 - c - (a + b - 2 * c + 3) * z)
r2 = (c - 1) * (c - 2) * (1 - z)
q = (a - c + 1) * (b - c + 1) * z
return (r1 * F1 + r2 * F2) / q
if (a, b, c) == (R12, 1, 2):
return (2 - 2 * sqrt(1 - z)) / z
if (a, b, c) == (1, 1, 2):
return -log(1 - z) / z
if (a, b, c) == (1, R32, R12):
return (1 + z) / (1 - z) ** 2
if (a, b, c) == (1, R32, 2):
return 2 * (1 / sqrt(1 - z) - 1) / z
if (a, b, c) == (R32, 2, R12):
return (1 + 3 * z) / (1 - z) ** 3
if (a, b, c) == (R32, 2, 1):
return (2 + z) / (2 * (sqrt(1 - z) * (1 - z) ** 2))
if (a, b, c) == (2, 2, 1):
return (1 + z) / (1 - z) ** 3
raise NotImplementedError
aa, bb = a
cc, = b
if z == 1:
return (gamma(cc) * gamma(cc - aa - bb) / gamma(cc - aa) /
gamma(cc - bb))
if ((aa * 2) in ZZ and (bb * 2) in ZZ and (cc * 2) in ZZ and
aa > 0 and bb > 0 and cc > 0):
try:
return _2f1(aa, bb, cc, z)
except NotImplementedError:
pass
return hyp
def _closed_form(hyp):
a, b, z = hyp.operands()
a, b = a.operands(), b.operands()
p, q = len(a), len(b)
if z == 0:
return Integer(1)
if p == q == 0:
return exp(z)
if p == 1 and q == 0:
return (1 - z)**(-a[0])
if p == 0 and q == 1:
# TODO: make this require only linear time
def _0f1(b, z):
F12 = cosh(2 * sqrt(z))
F32 = sinh(2 * sqrt(z)) / (2 * sqrt(z))
if 2 * b == 1:
return F12
if 2 * b == 3:
return F32
if 2 * b > 3:
return ((b - 2) * (b - 1) / z *
(_0f1(b - 2, z) - _0f1(b - 1, z)))
if 2 * b < 1:
return (_0f1(b + 1, z) + z / (b *
(b + 1)) * _0f1(b + 2, z))
raise ValueError
# Can evaluate 0F1 in terms of elementary functions when
# the parameter is a half-integer
if 2 * b[0] in ZZ and b[0] not in ZZ:
return _0f1(b[0], z)
# Confluent hypergeometric function
if p == 1 and q == 1:
aa, bb = a[0], b[0]
if aa * 2 == 1 and bb * 2 == 3:
t = sqrt(-z)
return sqrt(pi) / 2 * erf(t) / t
if a == 1 and b == 2:
return (exp(z) - 1) / z
n, m = aa, bb
if n in ZZ and m in ZZ and m > 0 and n > 0:
rf = rising_factorial
if m <= n:
return (exp(z) * sum(
rf(m - n, k) * (-z)**k / factorial(k) / rf(m, k)
for k in xrange(n - m + 1)))
else:
T = sum(
rf(n - m + 1, k) * z**k / (factorial(k) * rf(2 - m, k))
for k in xrange(m - n))
U = sum(
rf(1 - n, k) * (-z)**k / (factorial(k) * rf(2 - m, k))
for k in xrange(n))
return (factorial(m - 2) * rf(1 - m, n) * z**(1 - m) /
factorial(n - 1) * (T - exp(z) * U))
if p == 2 and q == 1:
R12 = QQ('1/2')
R32 = QQ('3/2')
def _2f1(a, b, c, z):
"""
Evaluation of 2F1(a, b, c, z), assuming a, b, c positive
integers or half-integers
"""
if b == c:
return (1 - z)**(-a)
if a == c:
return (1 - z)**(-b)
if a == 0 or b == 0:
return Integer(1)
if a > b:
a, b = b, a
if b >= 2:
F1 = _2f1(a, b - 1, c, z)
F2 = _2f1(a, b - 2, c, z)
q = (b - 1) * (z - 1)
return (((c - 2 * b + 2 + (b - a - 1) * z) * F1 +
(b - c - 1) * F2) / q)
if c > 2:
# how to handle this case?
if a - c + 1 == 0 or b - c + 1 == 0:
raise NotImplementedError
F1 = _2f1(a, b, c - 1, z)
F2 = _2f1(a, b, c - 2, z)
r1 = (c - 1) * (2 - c - (a + b - 2 * c + 3) * z)
r2 = (c - 1) * (c - 2) * (1 - z)
q = (a - c + 1) * (b - c + 1) * z
return (r1 * F1 + r2 * F2) / q
if (a, b, c) == (R12, 1, 2):
return (2 - 2 * sqrt(1 - z)) / z
if (a, b, c) == (1, 1, 2):
return -log(1 - z) / z
if (a, b, c) == (1, R32, R12):
return (1 + z) / (1 - z)**2
if (a, b, c) == (1, R32, 2):
return 2 * (1 / sqrt(1 - z) - 1) / z
if (a, b, c) == (R32, 2, R12):
return (1 + 3 * z) / (1 - z)**3
if (a, b, c) == (R32, 2, 1):
return (2 + z) / (2 * (sqrt(1 - z) * (1 - z)**2))
if (a, b, c) == (2, 2, 1):
return (1 + z) / (1 - z)**3
raise NotImplementedError
aa, bb = a
cc, = b
if z == 1:
return (gamma(cc) * gamma(cc - aa - bb) / gamma(cc - aa) /
gamma(cc - bb))
if ((aa * 2) in ZZ and (bb * 2) in ZZ and (cc * 2) in ZZ and aa > 0
and bb > 0 and cc > 0):
try:
return _2f1(aa, bb, cc, z)
except NotImplementedError:
pass
return hyp
def SingularityAnalysis(var,
zeta=1,
alpha=0,
beta=0,
delta=0,
precision=None,
normalized=True):
r"""
Return the asymptotic expansion of the coefficients of
an power series with specified pole and logarithmic singularity.
More precisely, this extracts the `n`-th coefficient
.. MATH::
[z^n] \left(\frac{1}{1-z/\zeta}\right)^\alpha
\left(\frac{1}{z/\zeta} \log \frac{1}{1-z/\zeta}\right)^\beta
\left(\frac{1}{z/\zeta} \log
\left(\frac{1}{z/\zeta} \log \frac{1}{1-z/\zeta}\right)\right)^\delta
(if ``normalized=True``, the default) or
.. MATH::
[z^n] \left(\frac{1}{1-z/\zeta}\right)^\alpha
\left(\log \frac{1}{1-z/\zeta}\right)^\beta
\left(\log
\left(\frac{1}{z/\zeta} \log \frac{1}{1-z/\zeta}\right)\right)^\delta
(if ``normalized=False``).
INPUT:
- ``var`` -- a string for the variable name.
- ``zeta`` -- (default: `1`) the location of the singularity.
- ``alpha`` -- (default: `0`) the pole order of the singularty.
- ``beta`` -- (default: `0`) the order of the logarithmic singularity.
- ``delta`` -- (default: `0`) the order of the log-log singularity.
Not yet implemented for ``delta != 0``.
- ``precision`` -- (default: ``None``) an integer. If ``None``, then
the default precision of the asymptotic ring is used.
- ``normalized`` -- (default: ``True``) a boolean, see above.
OUTPUT:
An asymptotic expansion.
EXAMPLES::
sage: asymptotic_expansions.SingularityAnalysis('n', alpha=1)
1
sage: asymptotic_expansions.SingularityAnalysis('n', alpha=2)
n + 1
sage: asymptotic_expansions.SingularityAnalysis('n', alpha=3)
1/2*n^2 + 3/2*n + 1
sage: _.parent()
Asymptotic Ring <n^ZZ> over Rational Field
::
sage: asymptotic_expansions.SingularityAnalysis('n', alpha=-3/2,
....: precision=3)
3/4/sqrt(pi)*n^(-5/2)
+ 45/32/sqrt(pi)*n^(-7/2)
+ 1155/512/sqrt(pi)*n^(-9/2)
+ O(n^(-11/2))
sage: asymptotic_expansions.SingularityAnalysis('n', alpha=-1/2,
....: precision=3)
-1/2/sqrt(pi)*n^(-3/2)
- 3/16/sqrt(pi)*n^(-5/2)
- 25/256/sqrt(pi)*n^(-7/2)
+ O(n^(-9/2))
sage: asymptotic_expansions.SingularityAnalysis('n', alpha=1/2,
....: precision=4)
1/sqrt(pi)*n^(-1/2)
- 1/8/sqrt(pi)*n^(-3/2)
+ 1/128/sqrt(pi)*n^(-5/2)
+ 5/1024/sqrt(pi)*n^(-7/2)
+ O(n^(-9/2))
sage: _.parent()
Asymptotic Ring <n^QQ> over Symbolic Constants Subring
::
sage: S = SR.subring(rejecting_variables=('n',))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=S.var('a'),
....: precision=4).map_coefficients(lambda c: c.factor())
1/gamma(a)*n^(a - 1)
+ (1/2*(a - 1)*a/gamma(a))*n^(a - 2)
+ (1/24*(3*a - 1)*(a - 1)*(a - 2)*a/gamma(a))*n^(a - 3)
+ (1/48*(a - 1)^2*(a - 2)*(a - 3)*a^2/gamma(a))*n^(a - 4)
+ O(n^(a - 5))
sage: _.parent()
Asymptotic Ring <n^(Symbolic Subring rejecting the variable n)>
over Symbolic Subring rejecting the variable n
::
sage: ae = asymptotic_expansions.SingularityAnalysis('n',
....: alpha=1/2, beta=1, precision=4); ae
1/sqrt(pi)*n^(-1/2)*log(n) + ((euler_gamma + 2*log(2))/sqrt(pi))*n^(-1/2)
- 5/8/sqrt(pi)*n^(-3/2)*log(n) + (1/8*(3*euler_gamma + 6*log(2) - 8)/sqrt(pi)
- (euler_gamma + 2*log(2) - 2)/sqrt(pi))*n^(-3/2) + O(n^(-5/2)*log(n))
sage: n = ae.parent().gen()
sage: ae.subs(n=n-1).map_coefficients(lambda x: x.canonicalize_radical())
1/sqrt(pi)*n^(-1/2)*log(n)
+ ((euler_gamma + 2*log(2))/sqrt(pi))*n^(-1/2)
- 1/8/sqrt(pi)*n^(-3/2)*log(n)
+ (-1/8*(euler_gamma + 2*log(2))/sqrt(pi))*n^(-3/2)
+ O(n^(-5/2)*log(n))
::
sage: asymptotic_expansions.SingularityAnalysis('n',
....: alpha=1, beta=1/2, precision=4)
log(n)^(1/2) + 1/2*euler_gamma*log(n)^(-1/2)
+ (-1/8*euler_gamma^2 + 1/48*pi^2)*log(n)^(-3/2)
+ (1/16*euler_gamma^3 - 1/32*euler_gamma*pi^2 + 1/8*zeta(3))*log(n)^(-5/2)
+ O(log(n)^(-7/2))
::
sage: ae = asymptotic_expansions.SingularityAnalysis('n',
....: alpha=0, beta=2, precision=14)
sage: n = ae.parent().gen()
sage: ae.subs(n=n-2)
2*n^(-1)*log(n) + 2*euler_gamma*n^(-1) - n^(-2) - 1/6*n^(-3) + O(n^(-5))
::
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=-1/2, beta=1, precision=2, normalized=False)
-1/2/sqrt(pi)*n^(-3/2)*log(n)
+ (-1/2*(euler_gamma + 2*log(2) - 2)/sqrt(pi))*n^(-3/2)
+ O(n^(-5/2)*log(n))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1/2, alpha=0, beta=1, precision=3, normalized=False)
2^n*n^(-1) + O(2^n*n^(-2))
ALGORITHM:
See [FS2009]_ together with the
`errata list <http://algo.inria.fr/flajolet/Publications/AnaCombi/errata.pdf>`_.
REFERENCES:
.. [FS2009] Philippe Flajolet and Robert Sedgewick,
`Analytic combinatorics <http://algo.inria.fr/flajolet/Publications/AnaCombi/book.pdf>`_.
Cambridge University Press, Cambridge, 2009.
TESTS::
sage: ex = asymptotic_expansions.SingularityAnalysis('n', alpha=-1/2,
....: precision=4)
sage: n = ex.parent().gen()
sage: coefficients = ((1-x)^(1/2)).series(
....: x, 21).truncate().coefficients(x, sparse=False)
sage: ex.compare_with_values(n, # rel tol 1e-6
....: lambda k: coefficients[k], [5, 10, 20])
[(5, 0.015778873294?), (10, 0.01498952777?), (20, 0.0146264622?)]
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=3, precision=2)
1/2*n^2 + 3/2*n + O(1)
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=3, precision=3)
1/2*n^2 + 3/2*n + 1
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=3, precision=4)
1/2*n^2 + 3/2*n + 1
::
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=0)
Traceback (most recent call last):
...
NotImplementedOZero: The error term in the result is O(0)
which means 0 for sufficiently large n.
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=-1)
Traceback (most recent call last):
...
NotImplementedOZero: The error term in the result is O(0)
which means 0 for sufficiently large n.
::
sage: asymptotic_expansions.SingularityAnalysis(
....: 'm', alpha=-1/2, precision=3)
-1/2/sqrt(pi)*m^(-3/2)
- 3/16/sqrt(pi)*m^(-5/2)
- 25/256/sqrt(pi)*m^(-7/2)
+ O(m^(-9/2))
sage: _.parent()
Asymptotic Ring <m^QQ> over Symbolic Constants Subring
Location of the singularity::
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=1, zeta=2, precision=3)
(1/2)^n
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=1, zeta=1/2, precision=3)
2^n
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=1, zeta=CyclotomicField(3).gen(),
....: precision=3)
(-zeta3 - 1)^n
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=4, zeta=2, precision=3)
1/6*(1/2)^n*n^3 + (1/2)^n*n^2 + 11/6*(1/2)^n*n + O((1/2)^n)
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=-1, zeta=2, precision=3)
Traceback (most recent call last):
...
NotImplementedOZero: The error term in the result is O(0)
which means 0 for sufficiently large n.
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=1/2, zeta=2, precision=3)
1/sqrt(pi)*(1/2)^n*n^(-1/2) - 1/8/sqrt(pi)*(1/2)^n*n^(-3/2)
+ 1/128/sqrt(pi)*(1/2)^n*n^(-5/2) + O((1/2)^n*n^(-7/2))
The following tests correspond to Table VI.5 in [FS2009]_. ::
sage: A.<n> = AsymptoticRing('n^QQ * log(n)^QQ', QQ)
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=-1/2, beta=1, precision=2,
....: normalized=False) * (- sqrt(pi*n^3))
1/2*log(n) + 1/2*euler_gamma + log(2) - 1 + O(n^(-1)*log(n))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=0, beta=1, precision=3,
....: normalized=False)
n^(-1) + O(n^(-2))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=0, beta=2, precision=14,
....: normalized=False) * n
2*log(n) + 2*euler_gamma - n^(-1) - 1/6*n^(-2) + O(n^(-4))
sage: (asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=1/2, beta=1, precision=4,
....: normalized=False) * sqrt(pi*n)).\
....: map_coefficients(lambda x: x.expand())
log(n) + euler_gamma + 2*log(2) - 1/8*n^(-1)*log(n) +
(-1/8*euler_gamma - 1/4*log(2))*n^(-1) + O(n^(-2)*log(n))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=1, beta=1, precision=13,
....: normalized=False)
log(n) + euler_gamma + 1/2*n^(-1) - 1/12*n^(-2) + 1/120*n^(-4)
+ O(n^(-6))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=1, beta=2, precision=4,
....: normalized=False)
log(n)^2 + 2*euler_gamma*log(n) + euler_gamma^2 - 1/6*pi^2
+ O(n^(-1)*log(n))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=3/2, beta=1, precision=3,
....: normalized=False) * sqrt(pi/n)
2*log(n) + 2*euler_gamma + 4*log(2) - 4 + 3/4*n^(-1)*log(n)
+ O(n^(-1))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=2, beta=1, precision=5,
....: normalized=False)
n*log(n) + (euler_gamma - 1)*n + log(n) + euler_gamma + 1/2
+ O(n^(-1))
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, alpha=2, beta=2, precision=4,
....: normalized=False) / n
log(n)^2 + (2*euler_gamma - 2)*log(n)
- 2*euler_gamma + euler_gamma^2 - 1/6*pi^2 + 2
+ n^(-1)*log(n)^2 + O(n^(-1)*log(n))
Be aware that the last result does *not* coincide with [FS2009]_,
they do have a different error term.
Checking parameters::
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, 1, 1/2, precision=0, normalized=False)
Traceback (most recent call last):
...
ValueError: beta and delta must be integers
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', 1, 1, 1, 1/2, normalized=False)
Traceback (most recent call last):
...
ValueError: beta and delta must be integers
::
sage: asymptotic_expansions.SingularityAnalysis(
....: 'n', alpha=0, beta=0, delta=1, precision=3)
Traceback (most recent call last):
...
NotImplementedError: not implemented for delta!=0
"""
from itertools import islice, count
from asymptotic_ring import AsymptoticRing
from growth_group import ExponentialGrowthGroup, \
MonomialGrowthGroup
from sage.arith.all import falling_factorial
from sage.categories.cartesian_product import cartesian_product
from sage.functions.other import binomial, gamma
from sage.calculus.calculus import limit
from sage.misc.cachefunc import cached_function
from sage.arith.srange import srange
from sage.rings.rational_field import QQ
from sage.rings.integer_ring import ZZ
from sage.symbolic.ring import SR
SCR = SR.subring(no_variables=True)
s = SR('s')
iga = 1 / gamma(alpha)
if iga.parent() is SR:
try:
iga = SCR(iga)
except TypeError:
pass
coefficient_ring = iga.parent()
if beta != 0:
coefficient_ring = SCR
@cached_function
def inverse_gamma_derivative(shift, r):
"""
Return value of `r`-th derivative of 1/Gamma
at alpha-shift.
"""
if r == 0:
result = iga * falling_factorial(alpha - 1, shift)
else:
result = limit((1 / gamma(s)).diff(s, r), s=alpha - shift)
try:
return coefficient_ring(result)
except TypeError:
return result
if isinstance(alpha, int):
alpha = ZZ(alpha)
if isinstance(beta, int):
beta = ZZ(beta)
if isinstance(delta, int):
delta = ZZ(delta)
if precision is None:
precision = AsymptoticRing.__default_prec__
if not normalized and not (beta in ZZ and delta in ZZ):
raise ValueError("beta and delta must be integers")
if delta != 0:
raise NotImplementedError("not implemented for delta!=0")
groups = []
if zeta != 1:
groups.append(ExponentialGrowthGroup((1 / zeta).parent(), var))
groups.append(MonomialGrowthGroup(alpha.parent(), var))
if beta != 0:
groups.append(
MonomialGrowthGroup(beta.parent(), 'log({})'.format(var)))
group = cartesian_product(groups)
A = AsymptoticRing(growth_group=group,
coefficient_ring=coefficient_ring,
default_prec=precision)
n = A.gen()
if zeta == 1:
exponential_factor = 1
else:
exponential_factor = n.rpow(1 / zeta)
if beta in ZZ and beta >= 0:
it = ((k, r) for k in count() for r in srange(beta + 1))
k_max = precision
else:
it = ((0, r) for r in count())
k_max = 0
if beta != 0:
log_n = n.log()
else:
# avoid construction of log(n)
# because it does not exist in growth group.
log_n = 1
it = reversed(list(islice(it, precision + 1)))
if normalized:
beta_denominator = beta
else:
beta_denominator = 0
L = _sa_coefficients_lambda_(max(1, k_max), beta=beta_denominator)
(k, r) = next(it)
result = (n**(-k) * log_n**(-r)).O()
if alpha in ZZ and beta == 0:
if alpha > 0 and alpha <= precision:
result = A(0)
elif alpha <= 0 and precision > 0:
from misc import NotImplementedOZero
raise NotImplementedOZero(A)
for (k, r) in it:
result += binomial(beta, r) * \
sum(L[(k, ell)] * (-1)**ell *
inverse_gamma_derivative(ell, r)
for ell in srange(k, 2*k+1)
if (k, ell) in L) * \
n**(-k) * log_n**(-r)
result *= exponential_factor * n**(alpha - 1) * log_n**beta
return result
