Noise budget above 0 in BFV example

[MarkusRa1]

Went through the bfv basics example, and came across this:

SEAL/native/examples/1_bfv_basics.cpp

Lines 298 to 321 in 1d5c816

	/*
	Finally, we multiply (x^2 + 1) * (x + 1)^2 * 2.
	*/
	print_line(__LINE__);
	cout << "Compute encrypted_result (2(x^2+1)(x+1)^2)." << endl;
	Ciphertext encrypted_result;
	Plaintext plain_two("2");
	evaluator.multiply_plain_inplace(x_sq_plus_one, plain_two);
	evaluator.multiply(x_sq_plus_one, x_plus_one_sq, encrypted_result);
	cout << " + size of encrypted_result: " << encrypted_result.size() << endl;
	cout << " + noise budget in encrypted_result: "
	<< decryptor.invariant_noise_budget(encrypted_result) << " bits" << endl;
	cout << "NOTE: Decryption can be incorrect if noise budget is zero." << endl;
	cout << endl;
	cout << "~~~~~~ A better way to calculate 2(x^2+1)(x+1)^2. ~~~~~~" << endl;
	/*
	Noise budget has reached 0, which means that decryption cannot be expected
	to give the correct result. This is because both ciphertexts x_sq_plus_one
	and x_plus_one_sq consist of 3 polynomials due to the previous squaring
	operations, and homomorphic operations on large ciphertexts consume much more
	noise budget than computations on small ciphertexts. Computing on smaller
	ciphertexts is also computationally significantly cheaper.

To me the comment seems to suggest that the noise budget should be 0 when the operations are done. However when I'm running them the noise budget end up on 7 to 10 bits.

[WeiDaiWD]

This was caused by some changes in code increasing noise budget, which is not a bad news. The issue is now fixed internally. You will see noise budget 0 in the next release. Thank you.