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✓ 3 results · all verified · 3 also independently AI-judged
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Model-based planning, Dyna, and model exploitation — Examples

1 · Prerequisites

2 · Logical flowchart

3 · Definitions, theorems and proofs

None yet.

4 · Examples, counterexamples and false statements

ExampleConstruction: AI-generatedVerification: AI-generatedprecheck pendingjudge pass (gpt-6-luna)Open item page →

An inaccurate model can give the exact return on behavior support

Example

Let S={s,g}, with one dummy action d at g and actions a,b at s. At g, action d has reward 0 and returns to g. At s, action a has reward 1 and moves to g, while action b returns to s with true reward 0 and learned reward 1. The true and learned models agree on (s,a) and (g,d). Let the supported set be B={(s,a),(g,d)}, let the initial state be s, and let H≥2. A policy that chooses a at s and d at g has identical true and learned H-step returns, although the learned model is wrong on the unsupported pair (s,b).

The TikZ diagram shows the two model transition/reward tables: a label u:r gives action u and its immediate reward on the arrow, and an arrow returning to its source denotes a self-transition. The learned reward for b is marked with a hat.

\begin{center} \begin{tikzpicture}[>=stealth, node distance=32mm] \node[circle,draw] (s) {s}; \node[circle,draw,right of=s] (g) {g}; \draw[->] (s) to[bend left=12] node[above] {a:1} (g); \draw[->] (g) to[loop right] node[right] {d:0} (g); \draw[->] (s) to[loop left] node[left] {b:0 (b^:1)} (s); \end{tikzpicture} \end{center}

Facts & Assumptions

Given: The two-state models, supported set, initial law, horizon, and policy in the Example.

[F1]

Finite learned transition and reward models: the true and learned reward means lie in [0,1], and each transition row is a probability distribution.

[F2]

Finite-horizon simulation bound for one fixed policy: for a common initial law and fixed Markov policy, uniform errors on the union of reachable pairs give the stated finite-horizon return bound.

Verification

Given: The finite models and policy in the Example.

1.1givenF1F2algebra

The true and learned occupancies under the policy place mass only on (s,a) at time 0 and on (g,d) at each later time. These pairs are exactly the listed supported pairs, and the models agree on both, so the reachable reward and transition errors are zero. Theorem [F2] applies with ϵr=ϵp=0.

2.1step 1.1F2algebra∎

Substitution into [F2] gives ∣JH−J^H∣≤0. Since an absolute value is nonnegative, JH=J^H. Directly, each return is 1 from the reward at the first step and 0 thereafter. Thus model errors outside the fixed policy's support do not affect this return.

ExampleConstruction: AI-generatedVerification: AI-generatedprecheck pendingjudge pass (gpt-6-luna)Open item page →

A small transition error accumulates over longer rollouts

Example

Let the states be u (safe) and v (failure), each with one action. Both true and learned rewards are 1 at u and 0 at v. The true model stays at u with probability 1, while the learned model moves from u to v with probability ϵ and stays at u with probability 1−ϵ, where 0<ϵ<1; both models keep v absorbing. Starting at u and following the only policy for horizon H, the true return is H and the learned return is ∑t=0H−1(1−ϵ)t.

The diagram compares the true transition model on the left with the learned transition model on the right. Nodes are states, and arrows carry transition probabilities; each state label gives its reward. The dashed arrow is present only in the learned model.

\begin{center} \begin{tikzpicture}[>=stealth, node distance=25mm] \node[circle,draw] (u1) {u, r=1}; \node[circle,draw,right of=u1] (v1) {v, r=0}; \draw[->] (u1) to[loop above] node[above] {1} (u1); \draw[->] (v1) to[loop right] node[right] {1} (v1); \node at (1.25,-0.8) {true}; \begin{scope}[xshift=7cm] \node[circle,draw] (u2) at (0,0) {u, r=1}; \node[circle,draw] (v2) at (2.8,0) {v, r=0}; \draw[->] (u2) to[loop above] node[above] {1−ϵ} (u2); \draw[->,dashed] (u2) to[bend left=12] node[above] {ϵ} (v2); \draw[->] (v2) to[loop right] node[right] {1} (v2); \node at (1.4,-0.8) {learned}; \end{scope} \end{tikzpicture} \end{center}

Facts & Assumptions

Given: The two-state models, initial state, policy, error parameter, and horizon in the Example.

[F1]

Finite learned transition and reward models: each model has probability transition rows and rewards in [0,1]; transition error is total variation.

[F2]

Finite-horizon simulation bound for one fixed policy: a fixed policy with zero reward error and transition error at most ϵ on its reachable pairs has return discrepancy at most (H2)ϵ from a common initial state.

Verification

Given: The finite model pair and policy in the Example.

1.1givenF1algebra

Under the true model, the state remains u, so each of the H rewards is 1 and JH=H. Under the learned model, the probability of occupying u at time t is (1−ϵ)t, by induction from the transition row, and the only positive reward is received at u. Hence J^H=∑t=0H−1(1−ϵ)t.

2.1givenF1F2step 1.1algebra∎

The reward error is zero. At u, the total variation between the true row (1,0) and learned row (1−ϵ,ϵ) is 12(ϵ+ϵ)=ϵ; at v the rows agree. Every reachable pair therefore satisfies the hypotheses of [F2], and H−J^H≤(H2)ϵ. The exact difference from step 1.1 is ∑t=0H−1[1−(1−ϵ)t], which is nondecreasing in H and is positive for H≥2. Thus even a fixed, small one-step transition error can produce a larger return discrepancy on longer rollouts, within the finite-horizon bound.

ExampleConstruction: AI-generatedVerification: AI-generatedprecheck pendingjudge pass (gpt-6-luna)Open item page →

A one-step optimizer selects a falsely rewarding unsupported action

Example

There is one state s, two actions asafe and aoff, and both actions return deterministically to s. Their true rewards are 1/2 and 0, respectively; their learned rewards are 1/2 and 1. Let H=1, let B={(s,asafe)}, and let the finite policy class contain the two policies that choose one action at time 0. Supply MPC with the ordered action listing (asafe,aoff) at s. Finite-horizon model-predictive control chooses aoff, whose predicted return is 1 and true return is 0, while the true best return in the class is 1/2.

The diagram uses a vertex for the state and a loop for each deterministic self-transition; each loop label gives the action and its true/learned immediate rewards.

\begin{center} \begin{tikzpicture}[>=stealth] \node[circle,draw] (s) at (0,0) {s}; \draw[->] (s) to[loop above] node[above] {asafe:1/2, r^=1/2} (s); \draw[->] (s) to[loop below] node[below] {aoff:0, r^=1} (s); \end{tikzpicture} \end{center}

Facts & Assumptions

Given: The one-state model pair, data set, horizon, and policy class in the Example.

[F1]

Model exploitation under support shift: a policy is model-optimal if it attains the learned return maximum in the finite policy class; off-support exploitation additionally requires positive learned occupancy on an unsupported pair, overprediction, and true suboptimality.

[F2]

Finite-horizon model-predictive control: at horizon one, the returned action maximizes the learned immediate reward, with the complete supplied action listing used only to break ties.

Verification

Given: The finite model pair and class in the Example.

1.1givenF2algebra

The two horizon-one learned returns are 1/2 and 1, so aoff is the unique learned optimizer and [F2] returns it. Its learned occupancy on (s,aoff) is 1, although this pair is outside B.

2.1givenF1step 1.1algebra∎

The true returns of asafe and aoff are 1/2 and 0. Thus the learned optimizer overpredicts its own return (1>0) and is truly suboptimal (0<1/2). All three clauses of [F1] hold, so this is off-support model exploitation as defined.