transform_from_ntt for Plaintext

[abeams]

Why does this not exist? The justification is as follows:

Suppose we have a database of plaintexts, such as in PIR. Because transform_to_ntt is a fairly expensive operation, we pre-process the entire database to convert all plaintexts to ntt form. But if we ever need the content of a plaintext, before doing any cryptographic operations, we essentially have to either 1) store a duplicate database in raw form or 2) multiple by a ciphertext of 1 and then decrypt (or some equally contrived technique).

[WeiDaiWD]

In BFV or BGV, the NTT form of a plaintext is much larger in size compared to its non-NTT form.