Evaluate cosine on a ciphertext

Evaluate cosine on a ciphertext

Usage

eval_cos(ct, a, b, degree)

Arguments

ct

A Ciphertext

a

Lower bound of the approximation interval

b

Upper bound of the approximation interval

degree

Chebyshev polynomial degree

Value

A Ciphertext holding the encrypted, slot-wise cosine of ct, approximated by a Chebyshev polynomial of the given degree on the interval [a, b]. Accuracy degrades outside that interval, and the result sits ceiling(log2(degree)) + 1 levels below ct.