The set of all prime numbers.
Prime.each(100) do |prime| p prime #=> 2, 3, 5, 7, 11, ...., 97 end
Prime is Enumerable:
Prime.first 5 # => [2, 3, 5, 7, 11]
Prime
.new is obsolete. Now Prime
has the default instance and you can access it as Prime
.instance.
For convenience, each instance method of Prime
.instance can be accessed as a class method of Prime
.
e.g.
Prime.instance.prime?(2) #=> true Prime.prime?(2) #=> true
A “generator” provides an implementation of enumerating pseudo-prime numbers and it remembers the position of enumeration and upper bound. Furthermore, it is an external iterator of prime enumeration which is compatible with an Enumerator.
Prime
::PseudoPrimeGenerator
is the base class for generators. There are few implementations of generator.
Prime
::EratosthenesGenerator
Uses eratosthenes' sieve.
Prime
::TrialDivisionGenerator
Uses the trial division method.
Prime
::Generator23
Generates all positive integers which are not divisible by either 2 or 3. This sequence is very bad as a pseudo-prime sequence. But this is faster and uses much less memory than the other generators. So, it is suitable for factorizing an integer which is not large but has many prime factors. e.g. for #prime? .
Returns the default instance of Prime.
# File lib/prime.rb, line 106 def instance; @the_instance end
obsolete. Use Prime
::instance
or class methods of Prime
.
# File lib/prime.rb, line 96 def initialize @generator = EratosthenesGenerator.new extend OldCompatibility warn "Prime::new is obsolete. use Prime::instance or class methods of Prime." end
Iterates the given block over all prime numbers.
ubound
Optional. An arbitrary positive number. The upper bound of enumeration. The method enumerates prime numbers infinitely if ubound
is nil.
generator
Optional. An implementation of pseudo-prime generator.
An evaluated value of the given block at the last time. Or an enumerator which is compatible to an Enumerator
if no block given.
Calls block
once for each prime number, passing the prime as a parameter.
ubound
Upper bound of prime numbers. The iterator stops after it yields all prime numbers p <= ubound
.
Prime
.new
returns an object extended by Prime
::OldCompatibility
in order to be compatible with Ruby 1.8, and Prime
#each is overwritten by Prime
::OldCompatibility
#each
.
Prime
.new
is now obsolete. Use Prime
.instance
.each
or simply Prime
.each
.
# File lib/prime.rb, line 147 def each(ubound = nil, generator = EratosthenesGenerator.new, &block) generator.upper_bound = ubound generator.each(&block) end
Re-composes a prime factorization and returns the product.
pd
Array of pairs of integers. The each internal pair consists of a prime number – a prime factor – and a natural number – an exponent.
For [[p_1, e_1], [p_2, e_2], ...., [p_n, e_n]]
, it returns:
p_1**e_1 * p_2**e_2 * .... * p_n**e_n. Prime.int_from_prime_division([[2,2], [3,1]]) #=> 12
# File lib/prime.rb, line 181 def int_from_prime_division(pd) pd.inject(1){|value, (prime, index)| value * prime**index } end
Returns true if value
is a prime number, else returns false.
value
an arbitrary integer to be checked.
generator
optional. A pseudo-prime generator.
# File lib/prime.rb, line 159 def prime?(value, generator = Prime::Generator23.new) return false if value < 2 for num in generator q,r = value.divmod num return true if q < num return false if r == 0 end end
Returns the factorization of value
.
value
An arbitrary integer.
generator
Optional. A pseudo-prime generator. generator
.succ must return the next pseudo-prime number in the ascending order. It must generate all prime numbers, but may also generate non prime numbers too.
ZeroDivisionError
when value
is zero.
For an arbitrary integer:
n = p_1**e_1 * p_2**e_2 * .... * p_n**e_n,
#prime_division(n) returns:
[[p_1, e_1], [p_2, e_2], ...., [p_n, e_n]]. Prime.prime_division(12) #=> [[2,2], [3,1]]
# File lib/prime.rb, line 211 def prime_division(value, generator = Prime::Generator23.new) raise ZeroDivisionError if value == 0 if value < 0 value = -value pv = [[-1, 1]] else pv = [] end for prime in generator count = 0 while (value1, mod = value.divmod(prime) mod) == 0 value = value1 count += 1 end if count != 0 pv.push [prime, count] end break if value1 <= prime end if value > 1 pv.push [value, 1] end return pv end
Ruby Core © 1993–2016 Yukihiro Matsumoto
Licensed under the Ruby License.
Ruby Standard Library © contributors
Licensed under their own licenses.