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# numpy.poly1d

class `numpy.``poly1d`(c_or_r, r=0, variable=None)

  A one-dimensional polynomial class.

  A convenience class, used to encapsulate “natural” operations on polynomials so that said operations may take on their customary form in code (see Examples).

  Parameters : | c_or_r : array_like The polynomial’s coefficients, in decreasing powers, or if the value of the second parameter is True, the polynomial’s roots (values where the polynomial evaluates to 0). For example, `poly1d([1, 2, 3])` returns an object that represents , whereas `poly1d([1, 2, 3], True)` returns one that represents . r : bool, optional If True, c_or_r specifies the polynomial’s roots; the default is False. variable : str, optional Changes the variable used when printing p from x to variable (see Examples).

  Examples

  Construct the polynomial :

      >>> p = np.poly1d([1, 2, 3])
      >>> print np.poly1d(p)
         2
      1 x + 2 x + 3

  Evaluate the polynomial at :

      >>> p(0.5)
      4.25

  Find the roots:

      >>> p.r
      array([-1.+1.41421356j, -1.-1.41421356j])
      >>> p(p.r)
      array([ -4.44089210e-16+0.j,  -4.44089210e-16+0.j])

  These numbers in the previous line represent (0, 0) to machine precision

  Show the coefficients:

      >>> p.c
      array([1, 2, 3])

  Display the order (the leading zero-coefficients are removed):

      >>> p.order
      2

  Show the coefficient of the k-th power in the polynomial (which is equivalent to `p.c[-(i+1)]`):

      >>> p[1]
      2

  Polynomials can be added, subtracted, multiplied, and divided (returns quotient and remainder):

      >>> p * p
      poly1d([ 1,  4, 10, 12,  9])

      >>> (p**3 + 4) / p
      (poly1d([  1.,   4.,  10.,  12.,   9.]), poly1d([ 4.]))

  `asarray(p)` gives the coefficient array, so polynomials can be used in all functions that accept arrays:

      >>> p**2 # square of polynomial
      poly1d([ 1,  4, 10, 12,  9])

      >>> np.square(p) # square of individual coefficients
      array([1, 4, 9])

  The variable used in the string representation of p can be modified, using the variable parameter:

      >>> p = np.poly1d([1,2,3], variable='z')
      >>> print p
         2
      1 z + 2 z + 3

  Construct a polynomial from its roots:

      >>> np.poly1d([1, 2], True)
      poly1d([ 1, -3,  2])

  This is the same polynomial as obtained by:

      >>> np.poly1d([1, -1]) * np.poly1d([1, -2])
      poly1d([ 1, -3,  2])

  Attributes

  `coeffs` |
  `order` |
  `variable` |

  Methods

  `deriv` |
  `integ` |

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