I have a finite automaton with no final/accepting states, so F is empty. How do I minimize it?
I got this on a test and I didn't know how to approach the problem because the automaton had no accepting states. Is a single initial state with all the transitions into itself the correct answer?
Your guess is correct and you can see it a little bit more formally as follows. Let $\mathcal{A} = (Q, A, \cdot, q_0, F)$ be a DFA. The Nerode congruence $\sim$ on $Q$ is defined as follows: $$ p \sim q \text{ if and only if, for every word $u \in A^*$, }\ p \cdot u \in F \iff q \cdot u \in F $$ The set of states of the minimal automaton of $\mathcal{A}$ is $Q/{\sim}$. Now if $F$ is the empty set, all the states of $Q$ are $\sim$-equivalent and thus $Q/{\sim}$ has only one element, say $Q/{\sim} = \{1\}$. You have no choice for the transitions and thus $1 \cdot a = 1$ for each letter $a$. Finally $1$ is the initial state, but there is no final state.
A finite automaton without end states denotes the language L = $ \emptyset $ . To minimize a DFA we minimize the number of states and the denoted language must be the same. By definition of DFA we must have an initial state $ q_0$ so $| Q | \geq 1$ and as you say we need to include the transition function with all transition into $ q_0 $ (because creating dead states is counterproductive).
