Polynomial factorization

The calculator finds all factors of a polynomial with rational coefficients

This page exists due to the efforts of the following people:


The calculator below find all irreducible factors of a polynomial with rational coefficients. To better understand how does it work switch on the 'Show details' toggle and read the description below the calculator.

PLANETCALC, Polynomial factorization with rational coefficients

Polynomial factorization with rational coefficients

Input polynomial

Rational polynomial factorization procedure1

  • Convert input polynomial in Q[x] to primitive polynomial in Z[x]
  • Find all square factors using Yun square-free factorization algorithm
  • For each square free factor of degree greater than 1 do the following steps
    • If leading coefficient is not equal to 1 then transform it to monic one using formula:
      v = a_n^{n-1}u(y/a_n)=\sum_{i=0}^{n-1} a_n^{n-1-i}a_iy^i+y^n, where
      v(y) - transformed monic polynomial,
      u(x) - original polynomial,
      an - leading coefficient of u(x),
      x = any
    • Find irreducible factors of v(y)=v1v2...vr in finite field Fp[x]
      • Find minimal prime number which is not divisor of v(y) discriminant
    • Use Hensel lifting to raise finite field order of the factorization to upper limit
      • Determine upper limit of target factors coefficients by formula:
        B=2^n\sqrt{n+i}||v||, where
        ||v||=max({|a_n|,...,|a_0|}) - maximum absolute value of polynomial coefficients (polynomial height)
      • Perform hensel lifting k\geq \frac{ln(2B)}{ln(p)} times
    • Check the factors by division v(y)/vi in Z[x], remove invalid factors
    • Invert monic polynomial transformation using formula:
      pp - primitive part function, which removes a content form an input polynomial

  1. Joel S. Cohen, Computer Algebra and Symbolyc Computation : Mathematical Methods, par. 9. Polynomial Factorization 

  2. Donald Knuth, The Art of Computer Programming vol.2 , par. 4.6.2 Factorization of Polynomials  

URL copied to clipboard
Creative Commons Attribution/Share-Alike License 3.0 (Unported) PLANETCALC, Polynomial factorization