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Preprints, Working Papers, ... Year : 2015

On the sign of a trigonometric expression


We propose a set of simple and fast algorithms for evalu-ating and using trigonometric expressions in the form F = d k=0 f k cos k π n , f k ∈ Q, d < n for a fixed n ∈ Z>0: comput-ing the sign of such an expression, evaluating it numerically and computing its minimal polynomial in Q[x]. As critical byproducts, we propose simple and efficient algorithms for performing arithmetic operations (multiplication, division, gcd) on polynomials expressed in a Chebyshev basis (with the same bit-complexity than in the monomial basis) and for computing the minimal polynomial of 2 cos π n in O(n 2 0) bit operations with n0 < n is the odd squarefree part of n. Within such a framework, we can decide if F = 0 in O(d(τ +d)) bit operations , compute the sign of F in O(d 2 τ) bit operations and compute the minimal polynomial of F in O(n 3 τ) bit operations, where τ denotes the maximum bit-size of the f k 's.
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hal-01108656 , version 1 (28-01-2015)


  • HAL Id : hal-01108656 , version 1


Pierre-Vincent Koseleff, Fabrice Rouillier, Cuong Tran. On the sign of a trigonometric expression. 2015. ⟨hal-01108656⟩
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