问Ruby/Rails:如何用科学符号显示数字？

EN

"%e" %x
=> 1.234560e+05

# Generate a long number
num = BigDecimal.new('123e+100')
#=> #<BigDecimal:1bca380,'0.123E1003',9(18)> 
num.to_s
#=> "123000000000000....
num.to_f
#=> 1.23e+102

# Convert BigDecimal to integer
int = num.to_i
#=> 123000000000000....
int.class
#=> Bignum
int.to_f
#=> 1.23e+102

class BigDecimal
  def to_sci(power_format='*10^%i')
    match_result = to_s.match(/0\.([0-9])([0-9]*)e([+-]?[0-9]*)/)

    int_part = match_result[1]
    float_part = match_result[2]
    exponent = match_result[3].to_i - 1

    significand = if float_part.empty?
                    int_part
                  else
                    "#{int_part}.#{float_part}"
                  end

    formatter = if negative?
                  "-%s#{power_format}"
                else
                  "%s#{power_format}"
                end

    formatter % [significand, exponent]
  end
end

require 'bigdecimal/util'

class Integer
  def to_sci(power_format='*10^%i')
    to_d.to_sci(power_notation)
  end
end

class Float
  def to_sci(power_format='*10^%i')
    to_d.to_sci(power_format)
  end
end

120.to_sci # Output: '1.2*10^2'
120.to_sci('\cdot 10^{%i}') # Output: '1.2\cdot 10^{2}'
0.05.to_sci('x10^%i') # Output: '5x10^-2'

def from_sci(str)
  BigDecimal(str.gsub(/[*xX]10\^/, 'e'))
end