class Prime

# File lib/prime.rb, line 212
def each(ubound = nil, generator = EratosthenesGenerator.new, &block)
  generator.upper_bound = ubound
  generator.each(&block)
end

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 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

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 lib/prime.rb, line 268
def int_from_prime_division(pd)
  pd.inject(1){|value, (prime, index)|
    value * prime**index
  }
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 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 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 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

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