Hello, I am using chebyshev approximation to evaluate exp(x). The problem is that, even though values are in the interval, results are messy. I am using 2^16 ring with security 128 bits, this is the key part of the code: vector<double> v = {-5, -4, -3, -2, -1, 0, 0.1, 0.2, 0.3, 1, 2, 3, 4, 5, 6, 7…

For the given range of values (-10,10) using only 27 degrees is insufficient. Try bumping it up by a lot and gradually reduce the degree to trade off between the accuracy and multiplication depth you want. openfhe-development/src/pke/examples/FUNCTION_EVALUATION.md at main · openfheorg/openfhe-deve…

Same happens with degree 200 and 288. Output with 288: (-2783.7, -2783.69, -2783.66, -2783.58, -2783.34, -2782.71, -2782.61, -2782.49, -2782.36, -2780.99, -2776.32, -2763.63, -2729.11, -2635.3, -2380.28, -1687.08, 197.247, -2782.71, -2782.71, -2782.71, -2782.71, ... I don’t think is related to th…

@marc-alonso Could you post your complete example here, including the cryptocontext parameters? exp grows fast with an argument (i.e., exponentially). It is important to know what multiplicative depth you are using. You may need room (extra levels) not to cause an overflow over your ciphertext/plain…

This is most likely a plaintext overflow. The CKKS plaintext isn’t an element of the ciphertext ring \mathbb{Z}[X]_{Q_{\ell}}/(X^{N}+1) (Q_{\ell} = \prod_{i=0}^{\ell} q_{i}), it is an element of \mathbb{R}[X]/(X^{N}+1), so to remain well define its infinity norm must remain small than Q_{\ell}/2 dur…

@marc-alonso Has the issue been resolved?

Weird behavior on Chebyshev

Library Questions

narger June 14, 2023, 10:36am 6

I suggest you to take advantage of the fact that e^x = (e^{x/10})^{10} and approximate e^{x/10} in [-1, 1] (it might take more levels but it is more stable for sure).

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Weird behavior on Chebyshev

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