polynomial to string

polynomial_to_s.rb

  POWERS = ['', '', '²', '³', '⁴'].freeze

  def poly_to_s(coefs)
    coefs.each_with_index.inject('') do |str, (coef, index)|
      term = if index == 4
               [coef]
             else
               [coef.positive? ? '+' : '-', ' ', coef.abs]
             end
      term << 'x' if index > 1
      term << POWERS[index]
      coef.zero? ? str : [term, ' ', str].join
  end.strip
  end

coefs = [-10.3, 24.7, 0.5086, -99.00003, -4.000002]
poly_to_s(coefs) # "-4.000002x⁴ - 99.00003x³ + 0.5086x² + 24.7 - 10.3"

def deriv_to_s(coefs)
  dcoefs = coefs[1..-1].map.with_index { |c, i| c * (i+1) }
  poly_to_s(dcoefs)
end