class Prime
The set of all prime numbers.
Example¶ ↑
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]
Retrieving the 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
Generators¶ ↑
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#prime?
.
Constants
- VERSION
Public Instance Methods
Iterates the given block over all prime numbers.
Parameters¶ ↑
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.
Return value¶ ↑
An evaluated value of the given block at the last time. Or an enumerator which is compatible to an Enumerator
if no block given.
Description¶ ↑
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
.
# File prime-0.1.2/lib/prime.rb, line 212 def each(ubound = nil, generator = EratosthenesGenerator.new, &block) generator.upper_bound = ubound generator.each(&block) end
Returns true if obj
is an Integer
and is prime. Also returns true if obj
is a Module that is an ancestor of Prime
. Otherwise returns false.
# File prime-0.1.2/lib/prime.rb, line 220 def include?(obj) case obj when Integer prime?(obj) when Module Module.instance_method(:include?).bind(Prime).call(obj) else false end end
Re-composes a prime factorization and returns the product.
For the decomposition:
[[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.
Parameters¶ ↑
pd
-
Array of pairs of integers. Each pair consists of a prime number – a prime factor – and a natural number – its exponent (multiplicity).
Example¶ ↑
Prime.int_from_prime_division([[3, 2], [5, 1]]) #=> 45 3**2 * 5 #=> 45
# File prime-0.1.2/lib/prime.rb, line 268 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. Integer#prime?
is much more performant.
Parameters¶ ↑
value
-
an arbitrary integer to be checked.
generator
-
optional. A pseudo-prime generator.
# File prime-0.1.2/lib/prime.rb, line 238 def prime?(value, generator = Prime::Generator23.new) raise ArgumentError, "Expected a prime generator, got #{generator}" unless generator.respond_to? :each raise ArgumentError, "Expected an integer, got #{value}" unless value.respond_to?(:integer?) && value.integer? return false if value < 2 generator.each do |num| q,r = value.divmod num return true if q < num return false if r == 0 end end
Returns the factorization of value
.
For an arbitrary integer:
p_1**e_1 * p_2**e_2 * ... * p_n**e_n,
prime_division
returns an array of pairs of integers:
[[p_1, e_1], [p_2, e_2], ..., [p_n, e_n]].
Each pair consists of a prime number – a prime factor – and a natural number – its exponent (multiplicity).
Parameters¶ ↑
value
-
An arbitrary integer.
generator
-
Optional. A pseudo-prime generator.
generator
.succ must return the next pseudo-prime number in ascending order. It must generate all prime numbers, but may also generate non-prime numbers, too.
Exceptions¶ ↑
ZeroDivisionError
-
when
value
is zero.
Example¶ ↑
Prime.prime_division(45) #=> [[3, 2], [5, 1]] 3**2 * 5 #=> 45
# File prime-0.1.2/lib/prime.rb, line 303 def prime_division(value, generator = Prime::Generator23.new) raise ZeroDivisionError if value == 0 if value < 0 value = -value pv = [[-1, 1]] else pv = [] end generator.each do |prime| 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 pv end