def fresnels(z):
"""Fresnel integral S, S(z)"""
if z == inf:
return mpf(0.5)
if z == -inf:
return mpf(-0.5)
return pi*z**3/6*hypsum([[3,4]],[],[],[[3,2],[7,4]],[],[],-pi**2*z**4/16)
def calculate_nome(k):
"""
Calculate the nome, q, from the value for k.
Useful factoids:
k**2 = m; m is used in Abramowitz
"""
k = convert_lossless(k)
if k > mpf('1'): # range error
raise ValueError
zero = mpf('0')
one = mpf('1')
if k == zero:
return zero
elif k == one:
return one
else:
kprimesquared = one - k**2
kprime = sqrt(kprimesquared)
top = ellipk(kprimesquared)
bottom = ellipk(k**2)
argument = mpf('-1') * pi * top / bottom
nome = exp(argument)
return nome
def calculate_nome(k):
"""
Calculate the nome, q, from the value for k.
Useful factoids:
k**2 = m; m is used in Abramowitz
"""
k = convert_lossless(k)
if k > mpf('1'): # range error
raise ValueError
zero = mpf('0')
one = mpf('1')
if k == zero:
return zero
elif k == one:
return one
else:
kprimesquared = one - k**2
kprime = sqrt(kprimesquared)
top = ellipk(kprimesquared)
bottom = ellipk(k**2)
argument = mpf('-1')*pi*top/bottom
nome = exp(argument)
return nome
def jacobi_elliptic_cn(u, m, verbose=False):
"""
Implements the jacobi elliptic cn function, using the expansion in
terms of q, from Abramowitz 16.23.2.
"""
u = convert_lossless(u)
m = convert_lossless(m)
if verbose:
print >> sys.stderr, '\nelliptic.jacobi_elliptic_cn'
print >> sys.stderr, '\tu: %1.12f' % u
print >> sys.stderr, '\tm: %1.12f' % m
zero = mpf('0')
onehalf = mpf('0.5')
one = mpf('1')
two = mpf('2')
if m == zero: # cn collapses to cos(u)
if verbose:
print >> sys.stderr, 'cn: special case, m == 0'
return cos(u)
elif m == one: # cn collapses to sech(u)
if verbose:
print >> sys.stderr, 'cn: special case, m == 1'
return sech(u)
else:
k = sqrt(m) # convert m to k
q = calculate_nome(k)
kprimesquared = one - k**2
kprime = sqrt(kprimesquared)
v = (pi * u) / (two*ellipk(k**2))
sum = zero
term = zero # series starts at zero
if verbose:
print >> sys.stderr, 'elliptic.jacobi_elliptic_cn: calculating'
while True:
factor1 = (q**(term + onehalf)) / (one + q**(two*term + one))
factor2 = cos((two*term + one)*v)
term_n = factor1*factor2
sum = sum + term_n
if verbose:
print >> sys.stderr, '\tTerm: %d' % term,
print >> sys.stderr, '\tterm_n: %e' % term_n,
print >> sys.stderr, '\tsum: %e' % sum
if not factor2 == zero:
#if log(term_n, '10') < -1*mpf.dps:
if abs(term_n) < eps:
break
term = term + one
answer = (two*pi) / (sqrt(m) * ellipk(k**2)) * sum
return answer
def chebcoeff(f,a,b,j,N):
s = mpf(0)
h = mpf(0.5)
for k in range(1, N+1):
t = cos(pi*(k-h)/N)
s += f(t*(b-a)*h + (b+a)*h) * cos(pi*j*(k-h)/N)
return 2*s/N
def calculate_k(q, verbose=False):
"""
Calculates the value of k for a particular nome, q.
Uses special cases of the jacobi theta functions, with
q as an argument, rather than m.
k = (v2(0, q)/v3(0, q))**2
"""
zero = mpf('0')
one = mpf('1')
q = convert_lossless(q)
if q > one or q < zero:
raise ValueError
# calculate v2(0, q)
sum = zero
term = zero # series starts at zero
while True:
factor1 = q**(term*(term + 1))
term_n = factor1 # suboptimal, kept for readability
sum = sum + term_n
if verbose:
print >> sys.stderr, '\tTerm: %d' % term,
print >> sys.stderr, '\tterm_n: %e' % term_n,
print >> sys.stderr, '\tsum: %e' % sum
if factor1 == zero: # all further terms will be zero
break
#if log(term_n, '10') < -1*mpf.dps:
if abs(term_n) < eps:
break
term = term + 1
v2 = 2*q**(mpf('0.25'))*sum
# calculate v3(0, q)
sum = zero
term = one # series starts at one
while True:
factor1 = q**(term*term)
term_n = factor1 # suboptimal, kept for readability
sum = sum + term_n
if factor1 == mpf('0'): # all further terms will be zero
break
#if log(term_n, '10') < -1*mpf.dps:
if abs(term_n) < eps:
break
term = term + 1
v3 = one + 2*sum
k = v2**2/v3**2
return k
def sumsh(f, interval, n=None, m=None):
"""
Sum f(k) for k = a, a+1, ..., b where [a, b] = interval,
using an n-term Shanks transformation. With m > 1, the Shanks
transformation is applied recursively m times.
Shanks summation often works well for slowly convergent and/or
alternating Taylor series.
"""
a, b = AS_POINTS(interval)
assert b == inf
if not n: n = 5 + int(mp.dps * 1.2)
if not m: m = 2 + n//3
orig = mp.prec
try:
mp.prec = 2*orig
s = mpf(0)
tbl = []
for k in range(a, a+n+m+2):
s += f(mpf(k))
tbl.append(s)
s = shanks_extrapolation(tbl, n, m)
finally:
mp.prec = orig
return +s
def chebyfit(f, interval, N, error=False):
"""
Chebyshev approximation: returns coefficients of a degree N-1
polynomial that approximates f on the interval [a, b]. With error=True,
also returns an estimate of the maximum error.
"""
a, b = AS_POINTS(interval)
orig = mp.prec
try:
mp.prec = orig + int(N**0.5) + 20
c = [chebcoeff(f,a,b,k,N) for k in range(N)]
d = [mpf(0)] * N
d[0] = -c[0]/2
h = mpf(0.5)
T = chebT(mpf(2)/(b-a), mpf(-1)*(b+a)/(b-a))
for k in range(N):
Tk = T.next()
for i in range(len(Tk)):
d[i] += c[k]*Tk[i]
d = d[::-1]
# Estimate maximum error
err = mpf(0)
for k in range(N):
x = cos(pi*k/N) * (b-a)*h + (b+a)*h
err = max(err, abs(f(x) - polyval(d, x)))
finally:
mp.prec = orig
if error:
return d, +err
else:
return d
def fresnelc(z):
"""Fresnel integral C, C(z)"""
if z == inf:
return mpf(0.5)
if z == -inf:
return mpf(-0.5)
return z*hypsum([[1,4]],[],[],[[1,2],[5,4]],[],[],-pi**2*z**4/16)
def jacobi_elliptic_cn(u, m, verbose=False):
"""
Implements the jacobi elliptic cn function, using the expansion in
terms of q, from Abramowitz 16.23.2.
"""
u = convert_lossless(u)
m = convert_lossless(m)
if verbose:
print >> sys.stderr, '\nelliptic.jacobi_elliptic_cn'
print >> sys.stderr, '\tu: %1.12f' % u
print >> sys.stderr, '\tm: %1.12f' % m
zero = mpf('0')
onehalf = mpf('0.5')
one = mpf('1')
two = mpf('2')
if m == zero: # cn collapses to cos(u)
if verbose:
print >> sys.stderr, 'cn: special case, m == 0'
return cos(u)
elif m == one: # cn collapses to sech(u)
if verbose:
print >> sys.stderr, 'cn: special case, m == 1'
return sech(u)
else:
k = sqrt(m) # convert m to k
q = calculate_nome(k)
kprimesquared = one - k**2
kprime = sqrt(kprimesquared)
v = (pi * u) / (two * ellipk(k**2))
sum = zero
term = zero # series starts at zero
if verbose:
print >> sys.stderr, 'elliptic.jacobi_elliptic_cn: calculating'
while True:
factor1 = (q**(term + onehalf)) / (one + q**(two * term + one))
factor2 = cos((two * term + one) * v)
term_n = factor1 * factor2
sum = sum + term_n
if verbose:
print >> sys.stderr, '\tTerm: %d' % term,
print >> sys.stderr, '\tterm_n: %e' % term_n,
print >> sys.stderr, '\tsum: %e' % sum
if not factor2 == zero:
#if log(term_n, '10') < -1*mpf.dps:
if abs(term_n) < eps:
break
term = term + one
answer = (two * pi) / (sqrt(m) * ellipk(k**2)) * sum
return answer
def estimate_error(self, results, prec, epsilon):
r"""
Given results from integrations `[I_1, I_2, \ldots, I_k]` done
with a quadrature of rule of degree `1, 2, \ldots, k`, estimate
the error of `I_k`.
For `k = 2`, we estimate `|I_{\infty}-I_2|` as `|I_2-I_1|`.
For `k > 2`, we extrapolate `|I_{\infty}-I_k| \approx |I_{k+1}-I_k|`
from `|I_k-I_{k-1}|` and `|I_k-I_{k-2}|` under the assumption
that each degree increment roughly doubles the accuracy of
the quadrature rule (this is true for both :class:`TanhSinh`
and :class:`GaussLegendre`). The extrapolation formula is given
by Borwein, Bailey & Girgensohn. Although not very conservative,
this method seems to be very robust in practice.
"""
if len(results) == 2:
return abs(results[0]-results[1])
try:
if results[-1] == results[-2] == results[-3]:
return mpf(0)
D1 = log(abs(results[-1]-results[-2]), 10)
D2 = log(abs(results[-1]-results[-3]), 10)
except ValueError:
return epsilon
D3 = -prec
D4 = min(0, max(D1**2/D2, 2*D1, D3))
return mpf(10) ** int(D4)
def estimate_error(self, results, prec, epsilon):
r"""
Given results from integrations `[I_1, I_2, \ldots, I_k]` done
with a quadrature of rule of degree `1, 2, \ldots, k`, estimate
the error of `I_k`.
For `k = 2`, we estimate `|I_{\infty}-I_2|` as `|I_2-I_1|`.
For `k > 2`, we extrapolate `|I_{\infty}-I_k| \approx |I_{k+1}-I_k|`
from `|I_k-I_{k-1}|` and `|I_k-I_{k-2}|` under the assumption
that each degree increment roughly doubles the accuracy of
the quadrature rule (this is true for both :class:`TanhSinh`
and :class:`GaussLegendre`). The extrapolation formula is given
by Borwein, Bailey & Girgensohn. Although not very conservative,
this method seems to be very robust in practice.
"""
if len(results) == 2:
return abs(results[0]-results[1])
try:
if results[-1] == results[-2] == results[-3]:
return mpf(0)
D1 = log(abs(results[-1]-results[-2]), 10)
D2 = log(abs(results[-1]-results[-3]), 10)
except ValueError:
return epsilon
D3 = -prec
D4 = min(0, max(D1**2/D2, 2*D1, D3))
return mpf(10) ** int(D4)
def calculate_k(q, verbose=False):
"""
Calculates the value of k for a particular nome, q.
Uses special cases of the jacobi theta functions, with
q as an argument, rather than m.
k = (v2(0, q)/v3(0, q))**2
"""
zero = mpf('0')
one = mpf('1')
q = convert_lossless(q)
if q > one or q < zero:
raise ValueError
# calculate v2(0, q)
sum = zero
term = zero # series starts at zero
while True:
factor1 = q**(term * (term + 1))
term_n = factor1 # suboptimal, kept for readability
sum = sum + term_n
if verbose:
print >> sys.stderr, '\tTerm: %d' % term,
print >> sys.stderr, '\tterm_n: %e' % term_n,
print >> sys.stderr, '\tsum: %e' % sum
if factor1 == zero: # all further terms will be zero
break
#if log(term_n, '10') < -1*mpf.dps:
if abs(term_n) < eps:
break
term = term + 1
v2 = 2 * q**(mpf('0.25')) * sum
# calculate v3(0, q)
sum = zero
term = one # series starts at one
while True:
factor1 = q**(term * term)
term_n = factor1 # suboptimal, kept for readability
sum = sum + term_n
if factor1 == mpf('0'): # all further terms will be zero
break
#if log(term_n, '10') < -1*mpf.dps:
if abs(term_n) < eps:
break
term = term + 1
v3 = one + 2 * sum
k = v2**2 / v3**2
return k
def fresnelc(z):
"""Fresnel integral C, C(z)"""
if z == inf:
return mpf(0.5)
if z == -inf:
return mpf(-0.5)
return z * hypsum([[1, 4]], [], [], [[1, 2], [5, 4]], [], [],
-pi**2 * z**4 / 16)
def fresnels(z):
"""Fresnel integral S, S(z)"""
if z == inf:
return mpf(0.5)
if z == -inf:
return mpf(-0.5)
return pi * z**3 / 6 * hypsum([[3, 4]], [], [], [[3, 2], [7, 4]], [], [],
-pi**2 * z**4 / 16)
def airyai(z):
"""Airy function, Ai(z)"""
if z == inf:
return 1/z
if z == -inf:
return mpf(0)
z3 = z**3 / 9
a = sum_hyp0f1_rat((2,3), z3) / (cbrt(9) * gamma(mpf(2)/3))
b = z * sum_hyp0f1_rat((4,3), z3) / (cbrt(3) * gamma(mpf(1)/3))
return a - b
def airyai(z):
"""Airy function, Ai(z)"""
if z == inf:
return 1 / z
if z == -inf:
return mpf(0)
z3 = z**3 / 9
a = sum_hyp0f1_rat((2, 3), z3) / (cbrt(9) * gamma(mpf(2) / 3))
b = z * sum_hyp0f1_rat((4, 3), z3) / (cbrt(3) * gamma(mpf(1) / 3))
return a - b
def sum_next(cls, prec, level, previous, f, verbose=False):
h = mpf(2)**(-level)
# Abscissas overlap, so reusing saves half of the time
if previous:
S = previous[-1] / (h * 2)
else:
S = mpf(0)
for x, w in cls.get_nodes(prec, level, verbose=False):
S += w * (f(NEG(x)) + f(x))
return h * S
def sum_next(cls, prec, level, previous, f, verbose=False):
h = mpf(2)**(-level)
# Abscissas overlap, so reusing saves half of the time
if previous:
S = previous[-1]/(h*2)
else:
S = mpf(0)
for x, w in cls.get_nodes(prec, level, verbose=False):
S += w*(f(NEG(x)) + f(x))
return h*S
def jacobi_elliptic_dn(u, m, verbose=False):
"""
Implements the jacobi elliptic cn function, using the expansion in
terms of q, from Abramowitz 16.23.3.
"""
u = convert_lossless(u)
m = convert_lossless(m)
if verbose:
print >> sys.stderr, '\nelliptic.jacobi_elliptic_dn'
print >> sys.stderr, '\tu: %1.12f' % u
print >> sys.stderr, '\tm: %1.12f' % m
zero = mpf('0')
onehalf = mpf('0.5')
one = mpf('1')
two = mpf('2')
if m == zero: # dn collapes to 1
return one
elif m == one: # dn collapses to sech(u)
return sech(u)
else:
k = sqrt(m) # convert m to k
q = calculate_nome(k)
v = (pi * u) / (two*ellipk(k**2))
sum = zero
term = one # series starts at one
if verbose:
print >> sys.stderr, 'elliptic.jacobi_elliptic_dn: calculating'
while True:
factor1 = (q**term) / (one + q**(two*term))
factor2 = cos(two*term*v)
term_n = factor1*factor2
sum = sum + term_n
if verbose:
print >> sys.stderr, '\tTerm: %d' % term,
print >> sys.stderr, '\tterm_n: %e' % term_n,
print >> sys.stderr, '\tsum: %e' % sum
if not factor2 == zero:
#if log(term_n, '10') < -1*mpf.dps:
if abs(term_n) < eps:
break
term = term + one
K = ellipk(k**2)
answer = (pi / (two*K)) + (two*pi*sum)/(ellipk(k**2))
return answer
def jacobi_elliptic_dn(u, m, verbose=False):
"""
Implements the jacobi elliptic cn function, using the expansion in
terms of q, from Abramowitz 16.23.3.
"""
u = convert_lossless(u)
m = convert_lossless(m)
if verbose:
print >> sys.stderr, '\nelliptic.jacobi_elliptic_dn'
print >> sys.stderr, '\tu: %1.12f' % u
print >> sys.stderr, '\tm: %1.12f' % m
zero = mpf('0')
onehalf = mpf('0.5')
one = mpf('1')
two = mpf('2')
if m == zero: # dn collapes to 1
return one
elif m == one: # dn collapses to sech(u)
return sech(u)
else:
k = sqrt(m) # convert m to k
q = calculate_nome(k)
v = (pi * u) / (two * ellipk(k**2))
sum = zero
term = one # series starts at one
if verbose:
print >> sys.stderr, 'elliptic.jacobi_elliptic_dn: calculating'
while True:
factor1 = (q**term) / (one + q**(two * term))
factor2 = cos(two * term * v)
term_n = factor1 * factor2
sum = sum + term_n
if verbose:
print >> sys.stderr, '\tTerm: %d' % term,
print >> sys.stderr, '\tterm_n: %e' % term_n,
print >> sys.stderr, '\tsum: %e' % sum
if not factor2 == zero:
#if log(term_n, '10') < -1*mpf.dps:
if abs(term_n) < eps:
break
term = term + one
K = ellipk(k**2)
answer = (pi / (two * K)) + (two * pi * sum) / (ellipk(k**2))
return answer
def airybi(z):
"""Airy function, Bi(z)"""
if z == inf:
return z
if z == -inf:
return mpf(0)
z3 = z**3 / 9
rt = nthroot(3, 6)
a = sum_hyp0f1_rat((2,3), z3) / (rt * gamma(mpf(2)/3))
b = z * rt * sum_hyp0f1_rat((4,3), z3) / gamma(mpf(1)/3)
return a + b
def airybi(z):
"""Airy function, Bi(z)"""
if z == inf:
return z
if z == -inf:
return mpf(0)
z3 = z**3 / 9
rt = nthroot(3, 6)
a = sum_hyp0f1_rat((2, 3), z3) / (rt * gamma(mpf(2) / 3))
b = z * rt * sum_hyp0f1_rat((4, 3), z3) / gamma(mpf(1) / 3)
return a + b
def transform_nodes(self, nodes, a, b, verbose=False):
r"""
Rescale standardized nodes (for `[-1, 1]`) to a general
interval `[a, b]`. For a finite interval, a simple linear
change of variables is used. Otherwise, the following
transformations are used:
.. math ::
[a, \infty] : t = \frac{1}{x} + (a-1)
[-\infty, b] : t = (b+1) - \frac{1}{x}
[-\infty, \infty] : t = \frac{x}{\sqrt{1-x^2}}
"""
a = mpmathify(a)
b = mpmathify(b)
one = mpf(1)
if (a, b) == (-one, one):
return nodes
half = mpf(0.5)
new_nodes = []
if (a, b) == (-inf, inf):
p05 = mpf(-0.5)
for x, w in nodes:
x2 = x*x
px1 = one-x2
spx1 = px1**p05
x = x*spx1
w *= spx1/px1
new_nodes.append((x, w))
elif a == -inf:
b1 = b+1
for x, w in nodes:
u = 2/(x+one)
x = b1-u
w *= half*u**2
new_nodes.append((x, w))
elif b == inf:
a1 = a-1
for x, w in nodes:
u = 2/(x+one)
x = a1+u
w *= half*u**2
new_nodes.append((x, w))
else:
# Simple linear change of variables
C = (b-a)/2
D = (b+a)/2
for x, w in nodes:
new_nodes.append((D+C*x, C*w))
return new_nodes
def transform_nodes(self, nodes, a, b, verbose=False):
r"""
Rescale standardized nodes (for `[-1, 1]`) to a general
interval `[a, b]`. For a finite interval, a simple linear
change of variables is used. Otherwise, the following
transformations are used:
.. math ::
[a, \infty] : t = \frac{1}{x} + (a-1)
[-\infty, b] : t = (b+1) - \frac{1}{x}
[-\infty, \infty] : t = \frac{x}{\sqrt{1-x^2}}
"""
a = mpmathify(a)
b = mpmathify(b)
one = mpf(1)
if (a, b) == (-one, one):
return nodes
half = mpf(0.5)
new_nodes = []
if (a, b) == (-inf, inf):
p05 = mpf(-0.5)
for x, w in nodes:
x2 = x*x
px1 = one-x2
spx1 = px1**p05
x = x*spx1
w *= spx1/px1
new_nodes.append((x, w))
elif a == -inf:
b1 = b+1
for x, w in nodes:
u = 2/(x+one)
x = b1-u
w *= half*u**2
new_nodes.append((x, w))
elif b == inf:
a1 = a-1
for x, w in nodes:
u = 2/(x+one)
x = a1+u
w *= half*u**2
new_nodes.append((x, w))
else:
# Simple linear change of variables
C = (b-a)/2
D = (b+a)/2
for x, w in nodes:
new_nodes.append((D+C*x, C*w))
return new_nodes
def transform(f, a, b):
"""
Given an integrand f defined over the interval [a, b], return an
equivalent integrand g defined on the standard interval [-1, 1].
If a and b are finite, this is achived by means of a linear change
of variables. If at least one point is infinite, the substitution
t = 1/x is used.
"""
a = convert_lossless(a)
b = convert_lossless(b)
if (a, b) == (-1, 1):
return f
one = mpf(1)
half = mpf(0.5)
# The transformation 1/x sends [1, inf] to [0, 1], which in turn
# can be transformed to [-1, 1] the usual way. For a double
# infinite interval, we simply evaluate the function symmetrically
if (a, b) == (-inf, inf):
# return transform(lambda x: (f(-1/x+1)+f(1/x-1))/x**2, 0, 1)
def y(x):
u = 2 / (x + one)
w = one - u
return half * (f(w) + f(-w)) * u**2
return y
if a == -inf:
# return transform(lambda x: f(-1/x+b+1)/x**2, 0, 1)
b1 = b + 1
def y(x):
u = 2 / (x + one)
return half * f(b1 - u) * u**2
return y
if b == inf:
# return transform(lambda x: f(1/x+a-1)/x**2, 0, 1)
a1 = a - 1
def y(x):
u = 2 / (x + one)
return half * f(a1 + u) * u**2
return y
# Simple linear change of variables
C = (b - a) / 2
D = (b + a) / 2
def g(x):
return C * f(D + C * x)
return g
def richardson_extrapolation(f, n, N):
if not callable(f):
g = f; f = lambda k: g.__getitem__(int(k))
orig = mp.prec
try:
mp.prec = 2*orig
s = mpf(0)
for j in range(0, N+1):
c = (n+j)**N * (-1)**(j+N) / (factorial(j) * factorial(N-j))
s += c * f(mpf(n+j))
finally:
mp.prec = orig
return +s
def sum_next(self, f, nodes, degree, prec, previous, verbose=False):
"""
Step sum for tanh-sinh quadrature of degree `m`. We exploit the
fact that half of the abscissas at degree `m` are precisely the
abscissas from degree `m-1`. Thus reusing the result from
the previous level allows a 2x speedup.
"""
h = mpf(2)**(-degree)
# Abscissas overlap, so reusing saves half of the time
if previous:
S = previous[-1]/(h*2)
else:
S = mpf(0)
S += fdot((w,f(x)) for (x,w) in nodes)
return h*S
def sum_next(self, f, nodes, degree, prec, previous, verbose=False):
"""
Step sum for tanh-sinh quadrature of degree `m`. We exploit the
fact that half of the abscissas at degree `m` are precisely the
abscissas from degree `m-1`. Thus reusing the result from
the previous level allows a 2x speedup.
"""
h = mpf(2)**(-degree)
# Abscissas overlap, so reusing saves half of the time
if previous:
S = previous[-1]/(h*2)
else:
S = mpf(0)
S += fdot((w,f(x)) for (x,w) in nodes)
return h*S
def estimate_error(cls, results, prec, epsilon):
"""
Estimate error of the calculation at the present level by
comparing it to the results from two previous levels. The
algorithm is given by Borwein, Bailey & Girgensohn.
"""
try:
if results[-1] == results[-2] == results[-3]:
return mpf(0)
D1 = log(abs(results[-1] - results[-2]), 10)
D2 = log(abs(results[-1] - results[-3]), 10)
except ValueError:
return epsilon
D3 = -prec
D4 = min(0, max(D1**2 / D2, 2 * D1, D3))
return mpf(10)**int(D4)
def summation(cls, f, points, prec, epsilon, max_level, verbose=False):
"""
Main summation function
"""
I = err = mpf(0)
for i in xrange(len(points)-1):
a, b = points[i], points[i+1]
if a == b:
continue
g = transform(f, a, b)
results = []
for level in xrange(1, max_level+1):
if verbose:
print "Integrating from %s to %s (level %s of %s)" % \
(nstr(a), nstr(b), level, max_level)
results.append(cls.sum_next(prec, level, results, g, verbose))
if level > 2:
err = cls.estimate_error(results, prec, epsilon)
if err <= epsilon:
break
if verbose:
print "Estimated error:", nstr(err)
I += results[-1]
if err > epsilon:
if verbose:
print "Failed to reach full accuracy. Estimated error:", nstr(err)
return I, err
def summation(cls, f, points, prec, epsilon, max_level, verbose=False):
"""
Main summation function
"""
I = err = mpf(0)
for i in xrange(len(points) - 1):
a, b = points[i], points[i + 1]
if a == b:
continue
g = transform(f, a, b)
results = []
for level in xrange(1, max_level + 1):
if verbose:
print "Integrating from %s to %s (level %s of %s)" % \
(nstr(a), nstr(b), level, max_level)
results.append(cls.sum_next(prec, level, results, g, verbose))
if level > 2:
err = cls.estimate_error(results, prec, epsilon)
if err <= epsilon:
break
if verbose:
print "Estimated error:", nstr(err)
I += results[-1]
if err > epsilon:
if verbose:
print "Failed to reach full accuracy. Estimated error:", nstr(
err)
return I, err
def diffc(f, x, n=1, radius=mpf(0.5)):
"""
Compute an approximation of the nth derivative of f at the point x
using the Cauchy integral formula. This only works for analytic
functions. A circular path with the given radius is used.
diffc increases the working precision slightly to avoid simple
rounding errors. Note that, especially for large n, differentiation
is extremely ill-conditioned, so this precaution does not
guarantee a correct result. (Provided there are no singularities
in the way, increasing the radius may help.)
The returned value will be a complex number; a large imaginary part
for a derivative that should be real may indicate a large numerical
error.
"""
prec = mp.prec
try:
mp.prec += 10
def g(t):
rei = radius*exp(j*t)
z = x + rei
return f(z) / rei**n
d = quadts(g, [0, 2*pi])
return d * factorial(n) / (2*pi)
finally:
mp.prec = prec
def stieltjes(n):
"""Computes the nth Stieltjes constant."""
n = int(n)
if n == 0:
return +euler
if n < 0:
raise ValueError("Stieltjes constants defined for n >= 0")
if n in stieltjes_cache:
prec, s = stieltjes_cache[n]
if prec >= mp.prec:
return +s
from quadrature import quadgl
def f(x):
r = exp(pi*j*x)
return (zeta(r+1) / r**n).real
orig = mp.prec
try:
p = int(log(factorial(n), 2) + 35)
mp.prec += p
u = quadgl(f, [-1, 1])
v = mpf(-1)**n * factorial(n) * u / 2
finally:
mp.prec = orig
stieltjes_cache[n] = (mp.prec, v)
return +v
def stieltjes(n):
"""Computes the nth Stieltjes constant."""
n = int(n)
if n == 0:
return +euler
if n < 0:
raise ValueError("Stieltjes constants defined for n >= 0")
if n in stieltjes_cache:
prec, s = stieltjes_cache[n]
if prec >= mp.prec:
return +s
from quadrature import quadgl
def f(x):
r = exp(pi * j * x)
return (zeta(r + 1) / r**n).real
orig = mp.prec
try:
p = int(log(factorial(n), 2) + 35)
mp.prec += p
u = quadgl(f, [-1, 1])
v = mpf(-1)**n * factorial(n) * u / 2
finally:
mp.prec = orig
stieltjes_cache[n] = (mp.prec, v)
return +v
def calc_nodes(cls, prec, level, verbose=False):
# It is important that the epsilon is set lower than the
# "real" epsilon
epsilon = ldexp(1, -prec - 8)
# Fairly high precision might be required for accurate
# evaluation of the roots
orig = mp.prec
mp.prec = int(prec * 1.5)
nodes = []
n = 3 * 2**(level - 1)
upto = n // 2 + 1
for j in xrange(1, upto):
# Asymptotic formula for the roots
r = mpf(math.cos(math.pi * (j - 0.25) / (n + 0.5)))
# Newton iteration
while 1:
t1, t2 = 1, 0
# Evaluates the Legendre polynomial using its defining
# recurrence relation
for j1 in xrange(1, n + 1):
t3, t2, t1 = t2, t1, ((2 * j1 - 1) * r * t1 -
(j1 - 1) * t2) / j1
t4 = n * (r * t1 - t2) / (r**2 - 1)
t5 = r
a = t1 / t4
r = r - a
if abs(a) < epsilon:
break
x = r
w = 2 / ((1 - r**2) * t4**2)
if verbose and j % 30 == 15:
print "Computing nodes (%i of %i)" % (j, upto)
nodes.append((x, w))
mp.prec = orig
return nodes
def estimate_error(cls, results, prec, epsilon):
"""
Estimate error of the calculation at the present level by
comparing it to the results from two previous levels. The
algorithm is given by Borwein, Bailey & Girgensohn.
"""
try:
if results[-1] == results[-2] == results[-3]:
return mpf(0)
D1 = log(abs(results[-1]-results[-2]), 10)
D2 = log(abs(results[-1]-results[-3]), 10)
except ValueError:
return epsilon
D3 = -prec
D4 = min(0, max(D1**2/D2, 2*D1, D3))
return mpf(10) ** int(D4)
def calc_nodes(cls, prec, level, verbose=False):
# It is important that the epsilon is set lower than the
# "real" epsilon
epsilon = ldexp(1, -prec-8)
# Fairly high precision might be required for accurate
# evaluation of the roots
orig = mp.prec
mp.prec = int(prec*1.5)
nodes = []
n = 3*2**(level-1)
upto = n//2 + 1
for j in xrange(1, upto):
# Asymptotic formula for the roots
r = mpf(math.cos(math.pi*(j-0.25)/(n+0.5)))
# Newton iteration
while 1:
t1, t2 = 1, 0
# Evaluates the Legendre polynomial using its defining
# recurrence relation
for j1 in xrange(1,n+1):
t3, t2, t1 = t2, t1, ((2*j1-1)*r*t1 - (j1-1)*t2)/j1
t4 = n*(r*t1- t2)/(r**2-1)
t5 = r
a = t1/t4
r = r - a
if abs(a) < epsilon:
break
x = r
w = 2/((1-r**2)*t4**2)
if verbose and j % 30 == 15:
print "Computing nodes (%i of %i)" % (j, upto)
nodes.append((x, w))
mp.prec = orig
return nodes
def transform(f, a, b):
"""
Given an integrand f defined over the interval [a, b], return an
equivalent integrand g defined on the standard interval [-1, 1].
If a and b are finite, this is achived by means of a linear change
of variables. If at least one point is infinite, the substitution
t = 1/x is used.
"""
a = convert_lossless(a)
b = convert_lossless(b)
if (a, b) == (-1, 1):
return f
one = mpf(1)
half = mpf(0.5)
# The transformation 1/x sends [1, inf] to [0, 1], which in turn
# can be transformed to [-1, 1] the usual way. For a double
# infinite interval, we simply evaluate the function symmetrically
if (a, b) == (-inf, inf):
# return transform(lambda x: (f(-1/x+1)+f(1/x-1))/x**2, 0, 1)
def y(x):
u = 2/(x+one)
w = one - u
return half * (f(w)+f(-w)) * u**2
return y
if a == -inf:
# return transform(lambda x: f(-1/x+b+1)/x**2, 0, 1)
b1 = b+1
def y(x):
u = 2/(x+one)
return half * f(b1-u) * u**2
return y
if b == inf:
# return transform(lambda x: f(1/x+a-1)/x**2, 0, 1)
a1 = a-1
def y(x):
u = 2/(x+one)
return half * f(a1+u) * u**2
return y
# Simple linear change of variables
C = (b-a)/2
D = (b+a)/2
def g(x):
return C * f(D + C*x)
return g
def calc_nodes(self, degree, prec, verbose=False):
"""
Calculates the abscissas and weights for Gauss-Legendre
quadrature of degree of given degree (actually `3 \cdot 2^m`).
"""
# It is important that the epsilon is set lower than the
# "real" epsilon
epsilon = ldexp(1, -prec-8)
# Fairly high precision might be required for accurate
# evaluation of the roots
orig = mp.prec
mp.prec = int(prec*1.5)
if degree == 1:
x = mpf(3)/5
w = mpf(5)/9
nodes = [(-x,w),(mpf(0),mpf(8)/9),(x,w)]
mp.prec = orig
return nodes
nodes = []
n = 3*2**(degree-1)
upto = n//2 + 1
for j in xrange(1, upto):
# Asymptotic formula for the roots
r = mpf(math.cos(math.pi*(j-0.25)/(n+0.5)))
# Newton iteration
while 1:
t1, t2 = 1, 0
# Evaluates the Legendre polynomial using its defining
# recurrence relation
for j1 in xrange(1,n+1):
t3, t2, t1 = t2, t1, ((2*j1-1)*r*t1 - (j1-1)*t2)/j1
t4 = n*(r*t1- t2)/(r**2-1)
t5 = r
a = t1/t4
r = r - a
if abs(a) < epsilon:
break
x = r
w = 2/((1-r**2)*t4**2)
if verbose and j % 30 == 15:
print "Computing nodes (%i of %i)" % (j, upto)
nodes.append((x, w))
nodes.append((NEG(x), w))
mp.prec = orig
return nodes
def calc_nodes(self, degree, prec, verbose=False):
"""
Calculates the abscissas and weights for Gauss-Legendre
quadrature of degree of given degree (actually `3 \cdot 2^m`).
"""
# It is important that the epsilon is set lower than the
# "real" epsilon
epsilon = ldexp(1, -prec-8)
# Fairly high precision might be required for accurate
# evaluation of the roots
orig = mp.prec
mp.prec = int(prec*1.5)
if degree == 1:
x = mpf(3)/5
w = mpf(5)/9
nodes = [(-x,w),(mpf(0),mpf(8)/9),(x,w)]
mp.prec = orig
return nodes
nodes = []
n = 3*2**(degree-1)
upto = n//2 + 1
for j in xrange(1, upto):
# Asymptotic formula for the roots
r = mpf(math.cos(math.pi*(j-0.25)/(n+0.5)))
# Newton iteration
while 1:
t1, t2 = 1, 0
# Evaluates the Legendre polynomial using its defining
# recurrence relation
for j1 in xrange(1,n+1):
t3, t2, t1 = t2, t1, ((2*j1-1)*r*t1 - (j1-1)*t2)/j1
t4 = n*(r*t1- t2)/(r**2-1)
t5 = r
a = t1/t4
r = r - a
if abs(a) < epsilon:
break
x = r
w = 2/((1-r**2)*t4**2)
if verbose and j % 30 == 15:
print "Computing nodes (%i of %i)" % (j, upto)
nodes.append((x, w))
nodes.append((NEG(x), w))
mp.prec = orig
return nodes
def secant(f, x0, x1=None, maxsteps=20, verbose=False):
"""Solve the equation f(x) = 0 using the secant method, starting
at the given initial point x0 and performing up to `maxsteps`
steps or quitting when the difference between successive x values
is smaller than the epsilon of the current working precision.
The secant method requires a second starting point x1 with both
x0 and x1 located close to the root. If only x0 is provided, x1
is automatically generated as x0 + 1/4."""
weps = 2*eps
x = x0 * mpf(1)
if x1 is None:
xprev = x0 + mpf(0.25)
else:
xprev = x1 * mpf(1)
deriv_prev = None
fxprev = f(xprev)
for i in xrange(maxsteps):
if verbose:
print "Step", i
print "x =", x
fx = f(x)
ydiff = fx - fxprev
xdiff = x - xprev
if verbose:
print "f(x) =", fx
print "xdiff = ", xdiff
print "ydiff = ", ydiff
try:
deriv = xdiff / ydiff
deriv_prev = deriv
except ZeroDivisionError:
if deriv_prev is None:
raise ZeroDivisionError(msg1)
if verbose and abs(xdiff) > weps:
print msg2
deriv = deriv_prev
x, xprev = x - fx*deriv, x
fxprev = fx
if verbose:
print
if abs(xdiff) <= weps:
break
return x
def polyval(coeffs, x, derivative=False):
"""
Given coefficients [cn, ..., c2, c1, c0], evaluate
P(x) = cn*x**n + ... + c2*x**2 + c1*x + c0.
If derivative=True is set, a tuple (P(x), P'(x)) is returned.
"""
if not coeffs:
return mpf(0)
p = mpnumeric(coeffs[0])
q = mpf(0)
for c in coeffs[1:]:
if derivative:
q = p + x*q
p = c + x*p
if derivative:
return p, q
else:
return p
def agm(a, b=1):
"""Arithmetic-geometric mean of a and b. Can be called with
a single argument, computing agm(a,1) = agm(1,a)."""
if not a or not b:
return a * b
weps = eps * 16
half = mpf(0.5)
while abs(a - b) > weps:
a, b = (a + b) * half, (a * b)**half
return a
def legendre(n, x):
"""Legendre polynomial P_n(x)."""
if isint(n):
n = int(n)
if x == -1:
# TODO: hyp2f1 should handle this
if x == int(x):
return (-1)**(n + (n >= 0)) * mpf(-1)
return inf
return hyp2f1(-n, n + 1, 1, (1 - x) / 2)
def legendre(n, x):
"""Legendre polynomial P_n(x)."""
if isint(n):
n = int(n)
if x == -1:
# TODO: hyp2f1 should handle this
if x == int(x):
return (-1)**(n + (n>=0)) * mpf(-1)
return inf
return hyp2f1(-n,n+1,1,(1-x)/2)
def agm(a, b=1):
"""Arithmetic-geometric mean of a and b. Can be called with
a single argument, computing agm(a,1) = agm(1,a)."""
if not a or not b:
return a*b
weps = eps * 16
half = mpf(0.5)
while abs(a-b) > weps:
a, b = (a+b)*half, (a*b)**half
return a
def exp_pade(a):
"""Exponential of a matrix using Pade approximants.
See G. H. Golub, C. F. van Loan 'Matrix Computations',
third Ed., page 572
TODO:
- find a good estimate for q
- reduce the number of matrix multiplications to improve
performance
"""
def eps_pade(p):
return mpf(2)**(3-2*p) * factorial(p)**2/(factorial(2*p)**2 * (2*p + 1))
q = 4
extraq = 8
while 1:
if eps_pade(q) < eps:
break
q += 1
q += extraq
j = max(1, int(log(mnorm(a,'inf'),2)))
extra = q
mp.dps += extra
try:
a = a/2**j
na = a.rows
den = eye(na)
num = eye(na)
x = eye(na)
c = mpf(1)
for k in range(1, q+1):
c *= mpf(q - k + 1)/((2*q - k + 1) * k)
x = a*x
cx = c*x
num += cx
den += (-1)**k * cx
f = lu_solve_mat(den, num)
for k in range(j):
f = f*f
finally:
mp.dps -= extra
return f
def exp_pade(a):
"""Exponential of a matrix using Pade approximants.
See G. H. Golub, C. F. van Loan 'Matrix Computations',
third Ed., page 572
TODO:
- find a good estimate for q
- reduce the number of matrix multiplications to improve
performance
"""
def eps_pade(p):
return mpf(2)**(3-2*p) * factorial(p)**2/(factorial(2*p)**2 * (2*p + 1))
q = 4
extraq = 8
while 1:
if eps_pade(q) < eps:
break
q += 1
q += extraq
j = max(1, int(log(mnorm(a,'inf'),2)))
extra = q
mp.dps += extra
try:
a = a/2**j
na = a.rows
den = eye(na)
num = eye(na)
x = eye(na)
c = mpf(1)
for k in range(1, q+1):
c *= mpf(q - k + 1)/((2*q - k + 1) * k)
x = a*x
cx = c*x
num += cx
den += (-1)**k * cx
f = lu_solve_mat(den, num)
for k in range(j):
f = f*f
finally:
mp.dps -= extra
return f
def findpoly(x, n=1):
"""Find an integer polynomial P of degree at most n such that
x is an approximate root of P."""
if x == 0:
return [1, 0]
xs = [mpf(1)]
for i in range(1, n + 1):
xs.append(x**i)
a = pslq(xs)
if a is not None:
return a[::-1]
def ei(z):
"""Exponential integral, Ei(z)"""
if z == inf:
return z
if z == -inf:
return -mpf(0)
v = z*hypsum([[1,1],[1,1]],[],[],[[2,1],[2,1]],[],[],z) + \
(log(z)-log(1/z))/2 + euler
if isinstance(z, mpf) and z < 0:
return v.real
return v
def limit(f, x, direction=-1, n=None, N=None):
"""Compute lim of f(t) as t -> x using Richardson extrapolation.
For infinite x, the function values [f(n), ... f(n+N)] are used.
For finite x, [f(x-direction/n)), ... f(x-direction/(n+N))] are
used. If x is inf, f can be also be a precomputed sequence
with a __getitem__ method."""
if callable(f):
if not n: n = 3 + int(mp.dps * 0.5)
if not N: N = 2*n
else:
# If a sequence, take as many terms are are available
g = f; f = lambda k: g.__getitem__(int(k))
if not N: N = len(g)-1
if not n: n = 0
if x == inf: return richardson_extrapolation(lambda k: f(mpf(k)), n, N)
elif x == -inf: return richardson_extrapolation(lambda k: f(mpf(-k)), n, N)
direction *= mpf(1)
def g(k):
return f(x - direction/(1+k))
return richardson_extrapolation(g, n, N)
