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pythonnumpypolynomials

numpy Polynomial to vector

How do I extract the coefficient vector from a numpy polynomial?

In Python, when using the numpy package to construct a polynomial, how do I extract the coefficients of this polynomial as a vector?

Solution

  • The numpy package has 2 classes of polynomial, the deprecated poly1d and the recommended Polynomial.

    Let's start with a vector that will become the source of the coefficients of our polynomial:

    v = [5, 18, -5]

    We can construct a Polynomial-class object:

    from numpy.polynomial import Polynomial
p = Polynomial(v)

    we can now obtain the coefficient vector again using coef

    p.coef

    Which gives:

    array([ 5., 18., -5.])

    The method for the deprecated poly1d class objects is the same (coef), but you would use poly1d instead of Polynomial to construct the polynial (which is not recommended anymore, you should use Polynomial).