/
series.py
1700 lines (1385 loc) · 48.6 KB
/
series.py
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"""
Lazy Power Series
This file provides an implementation of lazy univariate power
series, which uses the stream class for its internal data
structure. The lazy power series keep track of their approximate
order as much as possible without forcing the computation of any
additional coefficients. This is required for recursively defined
power series.
This code is based on the work of Ralf Hemmecke and Martin Rubey's
Aldor-Combinat, which can be found at
http://www.risc.uni-linz.ac.at/people/hemmecke/aldor/combinat/index.html.
In particular, the relevant section for this file can be found at
http://www.risc.uni-linz.ac.at/people/hemmecke/AldorCombinat/combinatse9.html.
"""
#*****************************************************************************
# Copyright (C) 2008 Mike Hansen <mhansen@gmail.com>,
#
# Distributed under the terms of the GNU General Public License (GPL)
#
# This code is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.
#
# The full text of the GPL is available at:
#
# http://www.gnu.org/licenses/
#*****************************************************************************
from stream import Stream, Stream_class
from series_order import bounded_decrement, increment, inf, unk
from sage.rings.all import Integer, prod
from functools import partial
from sage.misc.misc import repr_lincomb, is_iterator
from sage.algebras.algebra import Algebra
from sage.algebras.algebra_element import AlgebraElement
import sage.structure.parent_base
from sage.categories.all import Rings
class LazyPowerSeriesRing(Algebra):
def __init__(self, R, element_class = None, names=None):
"""
TESTS::
sage: from sage.combinat.species.series import LazyPowerSeriesRing
sage: L = LazyPowerSeriesRing(QQ)
sage: loads(dumps(L))
Lazy Power Series Ring over Rational Field
"""
#Make sure R is a ring with unit element
if not R in Rings():
raise TypeError, "Argument R must be a ring."
try:
z = R(Integer(1))
except StandardError:
raise ValueError, "R must have a unit element"
#Take care of the names
if names is None:
names = 'x'
else:
names = names[0]
self._element_class = element_class if element_class is not None else LazyPowerSeries
self._order = None
self._name = names
sage.structure.parent_base.ParentWithBase.__init__(self, R)
def ngens(self):
"""
EXAMPLES::
sage: LazyPowerSeriesRing(QQ).ngens()
1
"""
return 1
def __repr__(self):
"""
EXAMPLES::
sage: LazyPowerSeriesRing(QQ)
Lazy Power Series Ring over Rational Field
"""
return "Lazy Power Series Ring over %s"%self.base_ring()
def __cmp__(self, x):
"""
EXAMPLES::
sage: LQ = LazyPowerSeriesRing(QQ)
sage: LZ = LazyPowerSeriesRing(ZZ)
sage: LQ == LQ
True
sage: LZ == LQ
False
"""
if self.__class__ is not x.__class__:
return cmp(self.__class__, x.__class__)
return cmp(self.base_ring(), x.base_ring())
def _coerce_impl(self, x):
"""
EXAMPLES::
sage: L1 = LazyPowerSeriesRing(QQ)
sage: L2 = LazyPowerSeriesRing(RR)
sage: L2.has_coerce_map_from(L1)
True
sage: L1.has_coerce_map_from(L2)
False
::
sage: a = L1([1]) + L2([1])
sage: a.coefficients(3)
[2.00000000000000, 2.00000000000000, 2.00000000000000]
"""
return self(x)
def __call__(self, x=None, order=unk):
"""
EXAMPLES::
sage: from sage.combinat.species.stream import Stream
sage: L = LazyPowerSeriesRing(QQ)
sage: L()
Uninitialized lazy power series
sage: L(1)
1
sage: L(ZZ).coefficients(10)
[0, 1, -1, 2, -2, 3, -3, 4, -4, 5]
sage: L(iter(ZZ)).coefficients(10)
[0, 1, -1, 2, -2, 3, -3, 4, -4, 5]
sage: L(Stream(ZZ)).coefficients(10)
[0, 1, -1, 2, -2, 3, -3, 4, -4, 5]
::
sage: a = L([1,2,3])
sage: a.coefficients(3)
[1, 2, 3]
sage: L(a) is a
True
sage: L_RR = LazyPowerSeriesRing(RR)
sage: b = L_RR(a)
sage: b.coefficients(3)
[1.00000000000000, 2.00000000000000, 3.00000000000000]
sage: L(b)
Traceback (most recent call last):
...
TypeError: do not know how to coerce ... into self
TESTS::
sage: L(pi)
Traceback (most recent call last):
...
TypeError: do not know how to coerce pi into self
"""
cls = self._element_class
BR = self.base_ring()
if x is None:
res = cls(self, stream=None, order=unk, aorder=unk,
aorder_changed=True, is_initialized=False)
res.compute_aorder = uninitialized
return res
if isinstance(x, LazyPowerSeries):
x_parent = x.parent()
if x_parent.__class__ != self.__class__:
raise ValueError
if x_parent.base_ring() == self.base_ring():
return x
else:
if self.base_ring().has_coerce_map_from(x_parent.base_ring()):
return x._new(partial(x._change_ring_gen, self.base_ring()), lambda ao: ao, x, parent=self)
if hasattr(x, "parent") and BR.has_coerce_map_from(x.parent()):
x = BR(x)
return self.term(x, 0)
if hasattr(x, "__iter__") and not isinstance(x, Stream_class):
x = iter(x)
if is_iterator(x):
x = Stream(x)
if isinstance(x, Stream_class):
aorder = order if order != unk else 0
return cls(self, stream=x, order=order, aorder=aorder,
aorder_changed=False, is_initialized=True)
elif not hasattr(x, "parent"):
x = BR(x)
return self.term(x, 0)
raise TypeError, "do not know how to coerce %s into self"%x
def zero_element(self):
"""
Returns the zero power series.
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: L.zero_element()
0
"""
return self(self.base_ring()(0))
def identity_element(self):
"""
Returns the one power series.
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: L.identity_element()
1
"""
return self(self.base_ring()(1))
def gen(self, i=0):
"""
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: L.gen().coefficients(5)
[0, 1, 0, 0, 0]
"""
res = self._new_initial(1, Stream([0,1,0]))
res._name = self._name
return res
def term(self, r, n):
"""
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: L.term(0,0)
0
sage: L.term(3,2).coefficients(5)
[0, 0, 3, 0, 0]
"""
if n < 0:
raise ValueError, "n must be non-negative"
BR = self.base_ring()
if r == 0:
res = self._new_initial(inf, Stream([0]))
res._name = "0"
else:
zero = BR(0)
s = [zero]*n+[BR(r),zero]
res = self._new_initial(n, Stream(s))
if n == 0:
res._name = repr(r)
elif n == 1:
res._name = repr(r) + "*" + self._name
else:
res._name = "%s*%s^%s"%(repr(r), self._name, n)
return res
def _new_initial(self, order, stream):
"""
Returns a new power series with specified order.
INPUT:
- ``order`` - a non-negative integer
- ``stream`` - a Stream object
EXAMPLES::
sage: from sage.combinat.species.stream import Stream
sage: L = LazyPowerSeriesRing(QQ)
sage: L._new_initial(0, Stream([1,2,3,0])).coefficients(5)
[1, 2, 3, 0, 0]
"""
return self._element_class(self, stream=stream, order=order, aorder=order,
aorder_changed=False, is_initialized=True)
def _sum_gen(self, series_list):
"""
Returns a generator for the coefficients of the sum the the lazy
power series in series_list.
INPUT:
- ``series_list`` - a list of lazy power series
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: series_list = [ L([1]), L([0,1]), L([0,0,1]) ]
sage: g = L._sum_gen(series_list)
sage: [g.next() for i in range(5)]
[1, 2, 3, 3, 3]
"""
last_index = len(series_list) - 1
assert last_index >= 0
n = 0
while True:
r = sum( [f.coefficient(n) for f in series_list] )
yield r
n += 1
def sum(self, a):
"""
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: l = [L(ZZ)]*3
sage: L.sum(l).coefficients(10)
[0, 3, -3, 6, -6, 9, -9, 12, -12, 15]
"""
return self( self._sum_gen(a) )
#Potentially infinite sum
def _sum_generator_gen(self, g):
"""
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: s = L([1])
sage: def f():
... while True:
... yield s
sage: g = L._sum_generator_gen(f())
sage: [g.next() for i in range(10)]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
"""
s = Stream(g)
n = 0
while True:
r = s[n].coefficient(n)
for i in range(len(s)-1):
r += s[i].coefficient(n)
yield r
n += 1
def sum_generator(self, g):
"""
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: g = [L([1])]*6 + [L(0)]
sage: t = L.sum_generator(g)
sage: t.coefficients(10)
[1, 2, 3, 4, 5, 6, 6, 6, 6, 6]
::
sage: s = L([1])
sage: def g():
... while True:
... yield s
sage: t = L.sum_generator(g())
sage: t.coefficients(9)
[1, 2, 3, 4, 5, 6, 7, 8, 9]
"""
return self(self._sum_generator_gen(g))
#Potentially infinite product
def _product_generator_gen(self, g):
"""
EXAMPLES::
sage: from itertools import imap
sage: from sage.combinat.species.stream import _integers_from
sage: L = LazyPowerSeriesRing(QQ)
sage: g = imap(lambda i: L([1]+[0]*i+[1]), _integers_from(0))
sage: g2 = L._product_generator_gen(g)
sage: [g2.next() for i in range(10)]
[1, 1, 2, 4, 7, 12, 20, 33, 53, 84]
"""
z = g.next()
yield z.coefficient(0)
yield z.coefficient(1)
n = 2
for x in g:
z = z * x
yield z.coefficient(n)
n += 1
while True:
yield z.coefficient(n)
n += 1
def product_generator(self, g):
"""
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: s1 = L([1,1,0])
sage: s2 = L([1,0,1,0])
sage: s3 = L([1,0,0,1,0])
sage: s4 = L([1,0,0,0,1,0])
sage: s5 = L([1,0,0,0,0,1,0])
sage: s6 = L([1,0,0,0,0,0,1,0])
sage: s = [s1, s2, s3, s4, s5, s6]
sage: def g():
... for a in s:
... yield a
sage: p = L.product_generator(g())
sage: p.coefficients(26)
[1, 1, 1, 2, 2, 3, 4, 4, 4, 5, 5, 5, 5, 4, 4, 4, 3, 2, 2, 1, 1, 1, 0, 0, 0, 0]
::
sage: def m(n):
... yield 1
... while True:
... for i in range(n-1):
... yield 0
... yield 1
...
sage: def s(n):
... q = 1/n
... yield 0
... while True:
... for i in range(n-1):
... yield 0
... yield q
...
::
sage: def lhs_gen():
... n = 1
... while True:
... yield L(m(n))
... n += 1
...
::
sage: def rhs_gen():
... n = 1
... while True:
... yield L(s(n))
... n += 1
...
sage: lhs = L.product_generator(lhs_gen())
sage: rhs = L.sum_generator(rhs_gen()).exponential()
sage: lhs.coefficients(10)
[1, 1, 2, 3, 5, 7, 11, 15, 22, 30]
sage: rhs.coefficients(10)
[1, 1, 2, 3, 5, 7, 11, 15, 22, 30]
"""
return self(self._product_generator_gen(g))
class LazyPowerSeries(AlgebraElement):
def __init__(self, A, stream=None, order=None, aorder=None, aorder_changed=True, is_initialized=False, name=None):
"""
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: f = L()
sage: loads(dumps(f))
Uninitialized lazy power series
"""
AlgebraElement.__init__(self, A)
self._stream = stream
self.order = unk if order is None else order
self.aorder = unk if aorder is None else aorder
if self.aorder == inf:
self.order = inf
self.aorder_changed = aorder_changed
self.is_initialized = is_initialized
self._zero = A.base_ring().zero_element()
self._name = name
def compute_aorder(*args, **kwargs):
"""
The default compute_aorder does nothing.
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: a = L(1)
sage: a.compute_aorder() is None
True
"""
return None
def _get_repr_info(self, x):
"""
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: a = L([1,2,3])
sage: a.compute_coefficients(5)
sage: a._get_repr_info('x')
[('1', 1), ('x', 2), ('x^2', 3)]
"""
n = len(self._stream)
m = ['1', x]
m += [x+"^"+str(i) for i in range(2, n)]
c = [ self._stream[i] for i in range(n) ]
return [ (m,c) for m,c in zip(m,c) if c != 0]
def __repr__(self):
"""
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: s = L(); s._name = 's'; s
s
::
sage: L()
Uninitialized lazy power series
::
sage: a = L([1,2,3])
sage: a
O(1)
sage: a.compute_coefficients(2)
sage: a
1 + 2*x + 3*x^2 + O(x^3)
sage: a.compute_coefficients(4)
sage: a
1 + 2*x + 3*x^2 + 3*x^3 + 3*x^4 + 3*x^5 + ...
::
sage: a = L([1,2,3,0])
sage: a.compute_coefficients(5)
sage: a
1 + 2*x + 3*x^2
"""
if self._name is not None:
return self._name
if self.is_initialized:
n = len(self._stream)
x = self.parent()._name
baserepr = repr_lincomb(self._get_repr_info(x))
if self._stream.is_constant():
if self._stream[n-1] == 0:
l = baserepr
else:
l = baserepr + " + " + repr_lincomb([(x+"^"+str(i), self._stream[n-1]) for i in range(n, n+3)]) + " + ..."
else:
l = baserepr + " + O(x^%s)"%n if n > 0 else "O(1)"
else:
l = 'Uninitialized lazy power series'
return l
def refine_aorder(self):
"""
Refines the approximate order of self as much as possible without
computing any coefficients.
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: a = L([0,0,0,0,1])
sage: a.aorder
0
sage: a.coefficient(2)
0
sage: a.aorder
0
sage: a.refine_aorder()
sage: a.aorder
3
::
sage: a = L([0,0])
sage: a.aorder
0
sage: a.coefficient(5)
0
sage: a.refine_aorder()
sage: a.aorder
Infinite series order
::
sage: a = L([0,0,1,0,0,0])
sage: a[4]
0
sage: a.refine_aorder()
sage: a.aorder
2
"""
#If we already know the order, then we don't have
#to worry about the approximate order
if self.order != unk:
return
#aorder can never be infinity since order would have to
#be infinity as well
assert self.aorder != inf
if self.aorder == unk or not self.is_initialized:
self.compute_aorder()
else:
#Try to improve the approximate order
ao = self.aorder
c = self._stream
n = c.number_computed()
if ao == 0 and n > 0:
while ao < n:
if self._stream[ao] == 0:
self.aorder += 1
ao += 1
else:
self.order = ao
break
#Try to recognize the zero series
if ao == n:
#For non-constant series, we cannot do anything
if not c.is_constant():
return
if c[n-1] == 0:
self.aorder = inf
self.order = inf
return
if self.order == unk:
while ao < n:
if self._stream[ao] == 0:
self.aorder += 1
ao += 1
else:
self.order = ao
break
# if ao < n:
# self.order = ao
if hasattr(self, '_reference') and self._reference is not None:
self._reference._copy(self)
def initialize_coefficient_stream(self, compute_coefficients):
"""
Initializes the coefficient stream.
INPUT: compute_coefficients
TESTS::
sage: from sage.combinat.species.series_order import inf, unk
sage: L = LazyPowerSeriesRing(QQ)
sage: f = L()
sage: compute_coefficients = lambda ao: iter(ZZ)
sage: f.order = inf
sage: f.aorder = inf
sage: f.initialize_coefficient_stream(compute_coefficients)
sage: f.coefficients(5)
[0, 0, 0, 0, 0]
::
sage: f = L()
sage: compute_coefficients = lambda ao: iter(ZZ)
sage: f.order = 1
sage: f.aorder = 1
sage: f.initialize_coefficient_stream(compute_coefficients)
sage: f.coefficients(5)
[0, 1, -1, 2, -2]
"""
ao = self.aorder
assert ao != unk
if ao == inf:
self.order = inf
self._stream = Stream(0)
else:
self._stream = Stream(compute_coefficients(ao))
self.is_initialized = True
def compute_coefficients(self, i):
"""
Computes all the coefficients of self up to i.
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: a = L([1,2,3])
sage: a.compute_coefficients(5)
sage: a
1 + 2*x + 3*x^2 + 3*x^3 + 3*x^4 + 3*x^5 + ...
"""
self.coefficient(i)
def coefficients(self, n):
"""
Returns the first n coefficients of self.
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: f = L([1,2,3,0])
sage: f.coefficients(5)
[1, 2, 3, 0, 0]
"""
return [self.coefficient(i) for i in range(n)]
def is_zero(self):
"""
Returns True if and only if self is zero.
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: s = L([0,2,3,0])
sage: s.is_zero()
False
::
sage: s = L(0)
sage: s.is_zero()
True
::
sage: s = L([0])
sage: s.is_zero()
False
sage: s.coefficient(0)
0
sage: s.coefficient(1)
0
sage: s.is_zero()
True
"""
self.refine_aorder()
return self.order == inf
def set_approximate_order(self, new_order):
"""
Sets the approximate order of self and returns True if the
approximate order has changed otherwise it will return False.
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: f = L([0,0,0,3,2,1,0])
sage: f.get_aorder()
0
sage: f.set_approximate_order(3)
True
sage: f.set_approximate_order(3)
False
"""
self.aorder_changed = ( self.aorder != new_order )
self.aorder = new_order
return self.aorder_changed
def _copy(self, x):
"""
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: f = L.term(2, 2)
sage: g = L()
sage: g._copy(f)
sage: g.order
2
sage: g.aorder
2
sage: g.is_initialized
True
sage: g.coefficients(4)
[0, 0, 2, 0]
"""
self.order = x.order
self.aorder = x.aorder
self.aorder_changed = x.aorder_changed
self.compute_aorder = x.compute_aorder
self.is_initialized = x.is_initialized
self._stream = x._stream
def define(self, x):
"""
EXAMPLES: Test Recursive 0
::
sage: L = LazyPowerSeriesRing(QQ)
sage: one = L(1)
sage: monom = L.gen()
sage: s = L()
sage: s._name = 's'
sage: s.define(one+monom*s)
sage: s.aorder
0
sage: s.order
Unknown series order
sage: [s.coefficient(i) for i in range(6)]
[1, 1, 1, 1, 1, 1]
Test Recursive 1
::
sage: s = L()
sage: s._name = 's'
sage: s.define(one+monom*s*s)
sage: s.aorder
0
sage: s.order
Unknown series order
sage: [s.coefficient(i) for i in range(6)]
[1, 1, 2, 5, 14, 42]
Test Recursive 1b
::
sage: s = L()
sage: s._name = 's'
sage: s.define(monom + s*s)
sage: s.aorder
1
sage: s.order
Unknown series order
sage: [s.coefficient(i) for i in range(7)]
[0, 1, 1, 2, 5, 14, 42]
Test Recursive 2
::
sage: s = L()
sage: s._name = 's'
sage: t = L()
sage: t._name = 't'
sage: s.define(one+monom*t*t*t)
sage: t.define(one+monom*s*s)
sage: [s.coefficient(i) for i in range(9)]
[1, 1, 3, 9, 34, 132, 546, 2327, 10191]
sage: [t.coefficient(i) for i in range(9)]
[1, 1, 2, 7, 24, 95, 386, 1641, 7150]
Test Recursive 2b
::
sage: s = L()
sage: s._name = 's'
sage: t = L()
sage: t._name = 't'
sage: s.define(monom + t*t*t)
sage: t.define(monom + s*s)
sage: [s.coefficient(i) for i in range(9)]
[0, 1, 0, 1, 3, 3, 7, 30, 63]
sage: [t.coefficient(i) for i in range(9)]
[0, 1, 1, 0, 2, 6, 7, 20, 75]
Test Recursive 3
::
sage: s = L()
sage: s._name = 's'
sage: s.define(one+monom*s*s*s)
sage: [s.coefficient(i) for i in range(10)]
[1, 1, 3, 12, 55, 273, 1428, 7752, 43263, 246675]
"""
self._copy(x)
x._reference = self
def coefficient(self, n):
"""
Returns the coefficient of xn in self.
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: f = L(ZZ)
sage: [f.coefficient(i) for i in range(5)]
[0, 1, -1, 2, -2]
"""
# The following line must not be written n < self.get_aorder()
# because comparison of Integer and OnfinityOrder is not implemented.
if self.get_aorder() > n:
return self._zero
assert self.is_initialized
return self._stream[n]
def get_aorder(self):
"""
Returns the approximate order of self.
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: a = L.gen()
sage: a.get_aorder()
1
"""
self.refine_aorder()
return self.aorder
def get_order(self):
"""
Returns the order of self.
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: a = L.gen()
sage: a.get_order()
1
"""
self.refine_aorder()
return self.order
def get_stream(self):
"""
Returns self's underlying Stream object.
EXAMPLES::
sage: L = LazyPowerSeriesRing(QQ)
sage: a = L.gen()
sage: s = a.get_stream()
sage: [s[i] for i in range(5)]
[0, 1, 0, 0, 0]
"""
self.refine_aorder()
return self._stream
def _approximate_order(self, compute_coefficients, new_order, *series):
if self.is_initialized:
return
ochanged = self.aorder_changed
ao = new_order(*[s.aorder for s in series])
ao = inf if ao == unk else ao
tchanged = self.set_approximate_order(ao)
if len(series) == 0:
must_initialize_coefficient_stream = True
tchanged = ochanged = False
elif len(series) == 1 or len(series) == 2:
must_initialize_coefficient_stream = ( self.aorder == unk or self.is_initialized is False)
else:
raise ValueError
if ochanged or tchanged:
for s in series:
s.compute_aorder()
ao = new_order(*[s.aorder for s in series])
tchanged = self.set_approximate_order(ao)
if must_initialize_coefficient_stream:
self.initialize_coefficient_stream(compute_coefficients)
if hasattr(self, '_reference') and self._reference is not None:
self._reference._copy(self)
def _new(self, compute_coefficients, order_op, *series, **kwds):
parent = kwds['parent'] if 'parent' in kwds else self.parent()
new_fps = self.__class__(parent, stream=None, order=unk, aorder=self.aorder,
aorder_changed=True, is_initialized=False)
new_fps.compute_aorder = lambda: new_fps._approximate_order(compute_coefficients, order_op, *series)
return new_fps
def _add_(self, y):
"""
EXAMPLES: Test Plus 1