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Python class implementing a Sieve of Eratosthenes functionality for vector tuples
#!/usr/bin/env python3
#
# A "sieve of Eratosthenes" for integer vectors of length N.
#
# The original usage of this was for studying pythagorean triples and
# filtering out those that were simply multiples of smaller ones, e.g.
#
# (5, 12, 13) as a "fundamental" Pythagorean triple vs
# (10, 24, 26) as a multiple of (5, 12, 13)
#
# The code was then generalized to work for vectors of any length.
# Not sure entirely useful, but well here it is.
#
# Vector components MUST BE non-negative INTEGERS.
#
# Mandating integers makes vector equivalency simple; it's either an
# integer multiple or it isn't; vs otherwise needing to define an
# epsilon tolerance for floating point values.
#
# Mandating positive just makes things simpler and avoids questions
# such as: is (8, -8, 8) a multiple of (-1, 1, -1) and if so, what
# other reflections/transformation should be allowed? Our answer: none.
#
# You will (or should) note that this is kind of a backwards sieve, in
# that the has() method is reporting composites (multiples of a seed)
# and also the seeds themselves; don't use has() if you are looking for
# the "primes" ... it's really the seeds() method that will report back
# to you the remaining primes (see the tests code at bottom for an
# example of this).
#
# IMPLEMENTATION:
#
# Within the sieve vectors are stored in a dictionary using their
# tuple as the key. If the vector is a seed the value stored is
# another vector indicating how far up this seed has been sieved.
# If the vector is not a seed the value stored is irrelevant; it is
# merely the key presence that matters.
#
# Seeds are also recorded separately in __seeds so we can easily
# extend the sieve as necessary (without searching the entire sieve
# for the sieve vs. synthesized entries)
#
# The sieving is "somewhat" lazy. When you enter a seed we automatically
# sieve everything up to the point matching the magnitude of this new
# seed. After that we only sieve on demand based on magnitudes in the
# queries (the has() calls).
#
class VectorSieve:
# Create a sieve of dimension n.
# If you don't specify n it comes from the first vector you supply
def __init__(self, n=None):
self.__seeds = [] # the things you seeded (sort of; see _reseed)
self.__sieve = {} # the seeds plus their sieved multiples
self.__sievemxg = 0 # max magnitude sieved
self.__seeds_in_order = True
self.dimension = n
# Returns a copy of v as a tuple if v obeys all rules
# Raises ValueError if any rules not obeyed
#
# Rules enforced are:
# * Vector dimensionality must match sieve dimensionality
# * All components must be non-negative integers
#
def check(self, v):
n = len(v)
if n != self.dimension:
if self.dimension is None: # you didn't spec at init time
self.dimension = n # so just take this as gospel
else:
raise ValueError("dim(v)={} != {}".format(n, self.dimension))
# I suppose we could be more lenient here and accept int(c) == c
# which would permit things like 4.0 ... but it just seems like
# asking for trouble. For now integers enforced. I don't want to
# get into having to implement "epsilon" checking for floating ops.
for c in v:
if (not isinstance(c, int)) or (c < 0):
raise ValueError("vector components not non-negative integers")
return tuple(v)
# Add vector v into the sieve and (implicitly) sieve it.
#
def seed(self, v):
v = self.check(v) # throws ValueError if v illegal
vmg2 = VectorSieve._mg2(v)
# do nothing if we already have this one
if self.__has(v, vmg2):
return
# ok, it's a seed...
self.__seeds.append(v) # remember it for resieving
self.__sieve[v] = v # initial max multiple
# see if you've added out of magnitude order...
if self.__seeds_in_order and len(self.__seeds) > 1:
if vmg2 < VectorSieve._mg2(self.__seeds[-2]):
self.__seeds_in_order = False
# if this one is bigger than all previous...
if vmg2 > self.__sievemxg:
# everyone must be sieved up to here
self._resieve_all(vmg2)
else:
# just bring this guy up to snuff
self._resieve_this_vector(v, self.__sievemxg)
#
# Internal method used to extend sieving. Go through all the seeds
# and add more of their multiples until they are all sieved past
# the magnitude you are asking about
#
def _resieve_all(self, tarmg2):
for v in self.__seeds:
self._resieve_this_vector(v, tarmg2)
self.__sievemxg = tarmg2 # this is now the new largest
# Internal method: resieve one vector. Start where we left off
# and keep adding more multiples to the sieve until we get past
# the supplied target magnitude
#
def _resieve_this_vector(self, v, tarmg2):
vx = self.__sieve[v] # where it left off before
while VectorSieve._mg2(vx) < tarmg2:
# python2/python3 is why we need tuple() here...
vx = tuple(map(lambda i,j: i+j, vx, v))
self.__sieve[vx] = True # add this to the sieve
self.__sieve[v] = vx # update current highest
# Is the given vector in the sieve?
# Returns v if so else None.
#
def has(self, v):
return self.__has(self.check(v), VectorSieve._mg2(v))
# internal version that bypasses input checks and avoids
# having to recompute the squared-magnitude
#
def __has(self, v, vmg2):
# if you are asking beyond the point of where we've sieved so far...
if vmg2 > self.__sievemxg:
# go to double current max or just to here (if here is more)
self._resieve_all(max(vmg2, 2*self.__sievemxg))
try:
# it is the mere success of this lookup that implies we have it
x = self.__sieve[v]
return v
except KeyError:
return None
#
# Return v if the given vector is a "seed" else None.
#
# To be a seed v must:
# - have been explicitly seeded via seed()
# - AND not be a multiple of another seed
#
# This automatically _reseeds() for you if necessary so for example:
#
# v = VectorSieve(3)
# v.seed((6,8,10))
# s1 = v.is_seed((6,8,10))
# v.seed((3,4,5))
# s2 = v.is_seed((6,8,10))
#
# s1 will be (6,8,10) (i.e., not None) but s2 will be None because
# after the insert of (3,4,5) the vector (6,8,10) is no longer a seed
# (and: shame on you for adding seeds out of order)
#
def is_seed(self, v):
v = self.check(v)
self._reseed() # method does nothing if not necessary
return v if v in self.__seeds else None
#
# Eliminate any "false" seeds that came about if you put seeds
# into the sieve out of order. For example:
#
# v = VectorSieve()
# v.seed((6,8,10))
# v.seed((3,4,5))
#
# In this case the second seed means the first vector (6,8,10) should
# no longer be a seed. Really you aren't supposed to put vectors into
# sieve "out of order" like that, but just for grins we correct if you do.
#
# You shouldn't normally call this yourself; it's done transparently.
# And if you never put out-of-order seeds into the sieve then this
# never happens.
#
def _reseed(self):
if not self.__seeds_in_order:
# you added them out of order, so sieve the seeds!
seeds = sorted(self.__seeds, key=lambda v: VectorSieve._mg2(v))
v = VectorSieve(self.dimension)
for t in seeds:
v.seed(t)
v.__seeds_in_order = True # bcs we just did it
new_seeds = []
for t in seeds:
if v.is_seed(t):
new_seeds.append(t)
self.__seeds = new_seeds
self.__seeds_in_order = True
# Return the seeds.
# Returns a reseeded list (as a copy you can munge freely)
def seeds(self):
self._reseed()
return self.__seeds.copy()
# compute magnitude squared of a vector
@staticmethod
def _mg2(v):
x = 0
for c in v:
x += c*c
return x
#
# tests
#
if __name__ == "__main__":
general_tests = [
( 'init' , 4 ),
( 'seed' , (1,1,1,1) ),
( 'has' , (1,1,1,1) , (1,1,1,1) ),
( 'has' , (2,2,2,2) , (2,2,2,2) ),
( 'has' , (0,0,0,0) , None),
( 'has' , (0,1,1,2) , None),
( 'seed' , (9,9,9,9) ),
( 'is_seed', (1,1,1,1) , (1,1,1,1) ),
( 'is_seed', (2,2,2,2) , None),
( 'is_seed', (9,9,9,9) , None),
( 'init' , 4 ),
( 'has' , (2,2,2,2) , None ),
( 'has' , (0,0,0,0) , None),
( 'seed' , (9,9,9,9) ),
( 'has' , (2,2,2,2) , None ),
( 'has' , (0,0,0,0) , None),
( 'has' , (90,90,90,90) , (90,90,90,90) ),
( 'has' , (0,1,1,2) , None),
( 'seed' , (1,1,1,1) ),
( 'has' , (2,2,2,2) , (2,2,2,2) ),
( 'has' , (9,9,9,9) , (9,9,9,9) ),
( 'is_seed', (9,9,9,9) , None),
( 'has' , (1,1,1,1) , (1,1,1,1) ),
( 'is_seed', (1,1,1,1) , (1,1,1,1) ),
( 'is_seed', (2,2,2,2) , None),
( 'init' , 3),
( 'seed' , (60,80,100) ),
( 'has' , (6,8,10), None),
( 'has' , (600,800,1000), (600,800,1000) ),
( 'seed' , (3,4,5)),
( 'has' , (6,8,10), (6,8,10)),
( 'is_seed', (60, 80, 100), None),
( 'is_seed', (3,4,5), (3,4,5)),
( 'is_seed', (6,8,10), None),
( 'init' , None),
( 'seed' , (3,4,5)),
( 'has' , (3,4,5), (3,4,5)),
( 'seed' , (5,12,13)),
( 'has' , (5,12,13), (5,12,13)),
( 'has' , (50,120,130), (50,120,130)),
( 'has' , (30,40,50), (30,40,50)),
( 'init' , None),
( 'seed' , (5,12,13)),
( 'seed' , (3,4,5)),
( 'has' , (5,12,13), (5,12,13)),
( 'has' , (50,120,130), (50,120,130)),
( 'has' , (30,40,50), (30,40,50)),
( 'is_seed', (6,8,10), None),
( 'init' , 5),
( 'seed' , (0,0,1,0,0)),
( 'has' , (0,0,0,100,0), None),
( 'has' , (0,0,100,0,0), (0,0,100,0,0)),
( 'init' , 3),
( 'seed' , (6,8,10)),
( 'is_seed', (6,8,10), (6,8,10)),
( 'seed' , (3,4,5)),
( 'is_seed', (6,8,10), None)
]
v = None
for t in general_tests:
if t[0] == 'init':
v = VectorSieve(t[1])
elif t[0] == 'seed':
v.seed(t[1])
elif t[0] == 'has':
if v.has(t[1]) != t[2]:
print("FAIL: ", t)
exit(1)
elif t[0] == 'is_seed':
if v.is_seed(t[1]) != t[2]:
print("FAIL: ", t)
exit(1)
else:
print("WTF", t)
exit(1)
#
# Make a 1-dimensional sieve and actually do the sieve of E algorithm
# Check results against this table of primes that was generated with a
# different program (so as to actually have some verification attributes)
primes = ( 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47,
53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113,
127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191,
193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263,
269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 347,
349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419, 421,
431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499,
503, 509, 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593,
599, 601, 607, 613, 617, 619, 631, 641, 643, 647, 653, 659, 661,
673, 677, 683, 691, 701, 709, 719, 727, 733, 739, 743, 751, 757,
761, 769, 773, 787, 797, 809, 811, 821, 823, 827, 829, 839, 853,
857, 859, 863, 877, 881, 883, 887, 907, 911, 919, 929, 937, 941,
947, 953, 967, 971, 977, 983, 991, 997 )
primelimit = 1000
v = VectorSieve(1)
for i in range(2, primelimit):
v.seed((i,)) # force tuple vs just an int in parens
# at this point the true seeds should be the primes
seeds = v.seeds()
if len(primes) != len(seeds):
print("Wrong number of primes")
exit(1)
for p in primes:
if (p,) not in seeds:
print("Missing prime ", p)
exit(1)
# now try it again with dimensions varying N just for yucks, as follows:
for dm in range(2,10):
v = VectorSieve(dm)
z = [0] * dm
for i in range(2, primelimit):
z[-2] = i
v.seed(z)
seeds = v.seeds()
if len(primes) != len(seeds):
print("Wrong number of primes for dimension ",dm)
exit(1)
for p in primes:
z[-2] = p
if tuple(z) not in seeds:
print("Missing prime ", p, "at dim", dm)
exit(1)
# this variation puts multiple primes per tuple
for dm in range(6,20):
v = VectorSieve(dm)
z = [0] * dm
for i in range(2, primelimit):
z[-2] = i
z[-3] = i
z[-5] = i
z[0] = i
v.seed(z)
seeds = v.seeds()
if len(primes) != len(seeds):
print("Wrong number of primes for dimension ",dm)
exit(1)
for p in primes:
z[-2] = p
z[-3] = p
z[-5] = p
z[0] = p
if tuple(z) not in seeds:
print("Missing prime ", p, "at dim", dm)
exit(1)
print("All Tests Passed!")
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