def _eval_(self, x, y):
"""
EXAMPLES::
sage: gamma_inc(2.,0)
1.00000000000000
sage: gamma_inc(2,0)
1
sage: gamma_inc(1/2,2)
-sqrt(pi)*(erf(sqrt(2)) - 1)
sage: gamma_inc(1/2,1)
-sqrt(pi)*(erf(1) - 1)
sage: gamma_inc(1/2,0)
sqrt(pi)
sage: gamma_inc(x,0)
gamma(x)
sage: gamma_inc(1,2)
e^(-2)
sage: gamma_inc(0,2)
-Ei(-2)
"""
if y == 0:
return gamma(x)
if x == 1:
return exp(-y)
if x == 0:
return -Ei(-y)
if x == Rational((1, 2)): # only for x>0
from sage.functions.error import erf
return sqrt(pi) * (1 - erf(sqrt(y)))
return None
def _eval_(self, x, y):
"""
EXAMPLES::
sage: gamma_inc(2.,0)
1.00000000000000
sage: gamma_inc(2,0)
1
sage: gamma_inc(1/2,2)
-sqrt(pi)*(erf(sqrt(2)) - 1)
sage: gamma_inc(1/2,1)
-sqrt(pi)*(erf(1) - 1)
sage: gamma_inc(1/2,0)
sqrt(pi)
sage: gamma_inc(x,0)
gamma(x)
sage: gamma_inc(1,2)
e^(-2)
sage: gamma_inc(0,2)
-Ei(-2)
"""
if y == 0:
return gamma(x)
if x == 1:
return exp(-y)
if x == 0:
return -Ei(-y)
if x == Rational((1, 2)): # only for x>0
from sage.functions.error import erf
return sqrt(pi) * (1 - erf(sqrt(y)))
return None
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 range(n - m + 1)))
else:
T = sum(
rf(n - m + 1, k) * z**k / (factorial(k) * rf(2 - m, k))
for k in range(m - n))
U = sum(
rf(1 - n, k) * (-z)**k / (factorial(k) * rf(2 - m, k))
for k in range(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
range(n - m + 1)))
else:
T = sum(rf(n - m + 1, k) * z ** k /
(factorial(k) * rf(2 - m, k)) for k in
range(m - n))
U = sum(rf(1 - n, k) * (-z) ** k /
(factorial(k) * rf(2 - m, k)) for k in
range(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