Polynomial decomposition algorithms
Journal of Symbolic Computation
Rational function decomposition
ISSAC '91 Proceedings of the 1991 international symposium on Symbolic and algebraic computation
Decomposition of algebraic functions
Journal of Symbolic Computation
A polynomial decomposition algorithm
SYMSAC '76 Proceedings of the third ACM symposium on Symbolic and algebraic computation
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Determining whether a univariate polynomial may be written as the functional composition of two others of lower degree is a question that has been studied since at least the work of Ritt [1]. Algorithms by Barton and Zippel [2] and then by Kozen and Landau [3] have been incorporated in many computer algebra systems. Generalizations have been studied for functional decomposition of rational functions [4], algebraic functions [5], multivariate polynomials [6] and univariate Laurent polynomials [7]. We explore the functional decomposition problem for multivariate Laurent polynomials, considering the case f = g o h where g is univariate and h may be multivariate. We present an algorithm to find such a decomposition if it exists. The algorithm proceeds as follows: First, a variable weighting is chosen to make the weighted degree zero term in f constant. The positive degree and negative degree parts of h are then reconstructed separately, in a manner similar to that of Kozen and Landau, but by treating the homogeneous collections of terms by grade rather than individual monomials. Then terms of the univariate polynomial g are reconstructed degree by degree using a generic univariate projection of h.