# scipy.linalg.fiedler_companion

scipy.linalg.fiedler_companion(a)

  Returns a Fiedler companion matrix

  Given a polynomial coefficient array `a`, this function forms a pentadiagonal matrix with a special structure whose eigenvalues coincides with the roots of `a`.

  Parameters:
    a(N,) array_like

      1-D array of polynomial coefficients in descending order with a nonzero leading coefficient. For `N < 2`, an empty array is returned.

  Returns:
    c(N-1, N-1) ndarray

      Resulting companion matrix

  See also

  `companion`

  Notes

  Similar to `companion` the leading coefficient should be nonzero. In the case the leading coefficient is not 1, other coefficients are rescaled before the array generation. To avoid numerical issues, it is best to provide a monic polynomial.

  New in version 1.3.0.

  References

  [1]

  M. Fiedler, “ A note on companion matrices”, Linear Algebra and its Applications, 2003, DOI:10.1016/S0024-3795(03)00548-2

  Examples

      >>> import numpy as np
      >>> from scipy.linalg import fiedler_companion, eigvals
      >>> p = np.poly(np.arange(1, 9, 2))  # [1., -16., 86., -176., 105.]
      >>> fc = fiedler_companion(p)
      >>> fc
      array([[  16.,  -86.,    1.,    0.],
             [   1.,    0.,    0.,    0.],
             [   0.,  176.,    0., -105.],
             [   0.,    1.,    0.,    0.]])
      >>> eigvals(fc)
      array([7.+0.j, 5.+0.j, 3.+0.j, 1.+0.j])