# numpy.polynomial.polynomial.polyfromroots

polynomial.polynomial.polyfromroots(roots)

  Generate a monic polynomial with given roots.

  Return the coefficients of the polynomial

  \[p(x) = (x - r_0) * (x - r_1) * ... * (x - r_n),\]

  where the `r_n` are the roots specified in `roots`. If a zero has multiplicity n, then it must appear in `roots` n times. For instance, if 2 is a root of multiplicity three and 3 is a root of multiplicity 2, then `roots` looks something like [2, 2, 2, 3, 3]. The roots can appear in any order.

  If the returned coefficients are c, then

  \[p(x) = c_0 + c_1 * x + ... + x^n\]

  The coefficient of the last term is 1 for monic polynomials in this form.

  Parameters
    roots array_like

      Sequence containing the roots.

  Returns
    out ndarray

      1-D array of the polynomial’s coefficients If all the roots are real, then out is also real, otherwise it is complex. (see Examples below).

  See also

  `numpy.polynomial.chebyshev.chebfromroots`
  `numpy.polynomial.legendre.legfromroots`
  `numpy.polynomial.laguerre.lagfromroots`
  `numpy.polynomial.hermite.hermfromroots`
  `numpy.polynomial.hermite_e.hermefromroots`

  Notes

  The coefficients are determined by multiplying together linear factors of the form `(x - r_i)`, i.e.

  \[p(x) = (x - r_0) (x - r_1) ... (x - r_n)\]

  where `n == len(roots) - 1`; note that this implies that `1` is always returned for \(a_n\).

  Examples

      >>> from numpy.polynomial import polynomial as P
      >>> P.polyfromroots((-1,0,1)) # x(x - 1)(x + 1) = x^3 - x
      array([ 0., -1.,  0.,  1.])
      >>> j = complex(0,1)
      >>> P.polyfromroots((-j,j)) # complex returned, though values are real
      array([1.+0.j,  0.+0.j,  1.+0.j])

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