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# numpy.polymul

numpy.polymul(a1, a2)

  Find the product of two polynomials.

  Note

  This forms part of the old polynomial API. Since version 1.4, the new polynomial API defined in `numpy.polynomial` is preferred. A summary of the differences can be found in the transition guide.

  Finds the polynomial resulting from the multiplication of the two input polynomials. Each input must be either a poly1d object or a 1D sequence of polynomial coefficients, from highest to lowest degree.

  Parameters:
    a1, a2 array_like or poly1d object

      Input polynomials.

  Returns:
    out ndarray or poly1d object

      The polynomial resulting from the multiplication of the inputs. If either inputs is a poly1d object, then the output is also a poly1d object. Otherwise, it is a 1D array of polynomial coefficients from highest to lowest degree.

  See also

  `poly1d`

    A one-dimensional polynomial class.

  `poly`, `polyadd`, `polyder`, `polydiv`, `polyfit`, `polyint`, `polysub`, `polyval`
  `convolve`

    Array convolution. Same output as polymul, but has parameter for overlap mode.

  Examples

      >>> import numpy as np
      >>> np.polymul([1, 2, 3], [9, 5, 1])
      array([ 9, 23, 38, 17,  3])

  Using poly1d objects:

      >>> p1 = np.poly1d([1, 2, 3])
      >>> p2 = np.poly1d([9, 5, 1])
      >>> print(p1)
         2
      1 x + 2 x + 3
      >>> print(p2)
         2
      9 x + 5 x + 1
      >>> print(np.polymul(p1, p2))
         4      3      2
      9 x + 23 x + 38 x + 17 x + 3