Hello,
Thank you for your answer. The notion of modulus overflow is clearer now.
However, I still do not understand why modulus overflow happens during my Chebyshev interpolation. Indeed, to perform this operation I chose the multiplicative depth according to the table here : openfhe-development/src/pke/examples/FUNCTION_EVALUATION.md at main · openfheorg/openfhe-development · GitHub . I set my bounds to values such as [0.5; 3] (not too close to zero and over a small range) and varied the degree between 5 and 27. But I get only negative values and they are all very close together (similar to Weird behavior on Chebyshev). I solved that by increasing by one the multiplicative depth recommended in the table.
Still, many questions arise. Is there something wrong in my understanding of the table ? Why would a modulus overflow happen specifically when I perform a Chebyshev interpolation (function: 1/sqrt(x)) ? (By the way, if you have any clue about how the numbers in the table were obtained, do not hesitate to share.)
Thanks a lot for your help.