My question is with regards to the following (algorithmic) problem:
Problem. Given f∈Z[x,y],a,b∈Q,r∈Z, do there exist positive integers m,n such that f(m,n) = r a^m b^n?
Is this problem decidable? Is it decidable in any special case (e.g. taking a specific (non-trivial) f, taking a,b\in \mathbb{Z} or choosing specific a,b,r)?
Thank you!