How to use compress?

there is a function of compress,but there is no function of decompress.if I compress ciphertext,I will how to decompress

Compress is a way to reduce the size of a ciphertext before sending it to the decryption party (to minimize communication costs). Uncompress is not expected to be called in this scenario. One could “uncompress” a ciphertext by calling bootstrapping, e.g., when using CKKS bootstrapping. I would suggest looking at the documentation/examples for bootstrapping for more details.

Can you give an example?I don’t understand how to use bootstrapping for decompress?

You can look at to get familiar with CKKS bootstrapping.

I don’t understand the relationship between bootstrapping and compression。Is it possible to recover by bootstrapping after compression?

I suggest watching the Introduction to FHE webinar to get familiar with how noise increases in FHE with every computation (see slides 11-15). Eventually, no more computations are allowed. Bootstrapping is what resets the noise and enables more computations (by expanding the ciphertext). A compressed ciphertext is the one that does not support any more computations (and hence it can be much smaller).

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I understand it ,thank you!