Pretty Printing Polynomials ~ http://rubylearning.com/blog/2009/11/26/rpcfn-rubyfun-4/

polynomial.rb

class Polynomial
  def initialize(coefficients)
    @coefficients = coefficients.reverse # reverse so the index equates to the exponent of each coefficient
    raise ArgumentError, 'Need at least 2 coefficients' if coefficients.size < 2
  end
  def to_s
    # Build an array of sprintfs, LIFO to get most significant order
    @coefficients.inject([]) {|builder, coefficient| ["%+ix^%i" % [coefficient, builder.size]] + builder}.to_s.
    gsub(/(\+0x\^\d+|x\^0|\^1\d{0})/, ''). # Clean out 0x^y, x^0, ^1
    gsub(/\d{0}1x/, 'x').                  # Replace 1x with just x
    sub(/^\+/, '').                        # Remove leading +
    sub(/^$/, '0')                         # 0 when blank
  end
end

polynomial_test.rb

require 'test/unit'
require 'test/unit/ui/console/testrunner'
require 'polynomial'

class Polynomial_Test < Test::Unit::TestCase
  def setup
    @p1 = Polynomial.new([-3,-4,1,0,6])
    @p2 = Polynomial.new([1,0,2])
    @p3 = Polynomial.new([-1,-2,3,0])
    @p4 = Polynomial.new([0,0,0])
    @p5 = Polynomial.new([6,5,4,3,2,1])
    @p6 = Polynomial.new([0,5,4,3,2,1])
    @p7 = Polynomial.new([1,0])
    @p8 = Polynomial.new([1,0,0])
    @p9 = Polynomial.new([1,1,1,1,0])
  end

  def test_first_negative
    assert_equal("-3x^4-4x^3+x^2+6", @p1.to_s) 
  end

  def test_simple
    assert_equal("x^2+2", @p2.to_s) 
  end

  def test_first_minus_one
    assert_equal("-x^3-2x^2+3x", @p3.to_s)
  end
  
  def test_last_is_one
    assert_equal("6x^5+5x^4+4x^3+3x^2+2x+1", @p5.to_s)
  end
  
  def test_zero_up_front
    assert_equal("5x^4+4x^3+3x^2+2x+1", @p6.to_s)
  end
  
  def test_lots_of_ones
    assert_equal("x^4+x^3+x^2+x", @p9.to_s)
  end
  
  
  def test_short
    assert_equal("x", @p7.to_s)
  end

  def test_all_zero
    assert_equal("0", @p4.to_s)
  end
  
  def test_last_two_zero
    assert_equal("x^2", @p8.to_s)
  end

  def test_error
    e = assert_raise(ArgumentError) { Polynomial.new([1]) }
    assert_match(/Need at least 2 coefficients/, e.message)
  end
end

Test::Unit::UI::Console::TestRunner.run(Polynomial_Test)