eval_powers: Evaluate several series on one ciphertext

In openfhe.R: R Interface to the 'OpenFHE' Fully Homomorphic Encryption Library

Evaluate several series on one ciphertext

Description

Evaluating a polynomial or a Chebyshev series on a ciphertext spends most of its time computing the powers (or the Chebyshev polynomials) of the ciphertext. These functions separate the two steps, so that several series can be evaluated on the same ciphertext for the cost of one set of powers (CKKS only).

Usage

eval_powers(ct, coefficients)

eval_poly_with_precomp(powers, coefficients)

eval_cheby_polys(ct, coefficients, a, b)

eval_chebyshev_series_with_precomp(polys, coefficients)

Arguments

ct	A Ciphertext.
coefficients	Integer, double or complex vector of coefficients, constant term first, as for eval_poly() and eval_chebyshev(). Pass whole-number Chebyshev coefficients as doubles; see eval_chebyshev().
powers	A SeriesPowers object from eval_powers().
a, b	Numeric; the interval of the Chebyshev approximation.
polys	A SeriesPowers object from eval_cheby_polys().

Details

eval_powers() computes the powers that eval_poly() would compute for coefficients, and eval_poly_with_precomp() evaluates a polynomial from them. eval_cheby_polys() and eval_chebyshev_series_with_precomp() are the same pair for eval_chebyshev().

The precomputation depends on coefficients only through the degree (the length of the vector), so it can be reused for any series of that degree. Below degree 5 only the powers with a nonzero coefficient are computed, so there the nonzero terms must match as well.

Value

eval_powers() and eval_cheby_polys(): a SeriesPowers object. The other two: a Ciphertext.

Examples

cc <- fhe_context("CKKS", multiplicative_depth = 4L, scaling_mod_size = 50L,
                  batch_size = 8L, features = Feature$ADVANCEDSHE)
keys <- key_gen(cc, eval_mult = TRUE)
ct <- encrypt(keys@public, make_ckks_packed_plaintext(cc, c(0.5, 1, 2)), cc = cc)
p <- c(1, 0, 2, 0, 0, 1)
q <- c(0, 1, 0, 3, 0, -1)
powers <- eval_powers(ct, p)
ct_p <- eval_poly_with_precomp(powers, p)
ct_q <- eval_poly_with_precomp(powers, q)

openfhe.R documentation built on Nov. 13, 2026, 5:07 p.m.