Plackett-Luce Selection Probability Formula
In the Plackett-Luce model, the probability of selecting a specific response from a set of possible responses given an input , is calculated by normalizing its "worth" value, . The selection probability is the worth of the selected response divided by the sum of the worths of all possible responses:

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Ch.4 Alignment - Foundations of Large Language Models
Foundations of Large Language Models
Foundations of Large Language Models Course
Computing Sciences
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Plackett-Luce Selection Probability Formula
Optimal Policy as a Product of Reference Policy and Exponentiated Reward
Worth Function in Plackett-Luce Model
A language model's policy, which determines the probability of generating an output
ygiven an inputx, is structured to be proportional to the exponential of a reward scorer(x, y). For a specific input, two potential outputs have the following reward scores:- Output A: Reward = 3.0
- Output B: Reward = 1.0
Based on this formulation, how does the probability of generating Output A compare to the probability of generating Output B?
Analyzing Language Model Response Probabilities
A language model's policy is designed such that the probability of generating an output is proportional to the exponential of its reward score. If Output Y has a reward score that is exactly double the reward score of Output Z, it means the policy will assign exactly double the probability to Output Y compared to Output Z.
Plackett-Luce Selection Probability Formula
A system assigns a 'worth' value to potential text completions, calculated as the exponential of a reward score. Initially, three completions (A, B, C) have reward scores of 2.0, 3.0, and 4.0, respectively. If the reward score for each completion is increased by a constant value of 1.0, how does this change affect the ratio of worth between any two completions (e.g., the ratio of worth(B) to worth(A))?
Calculating Response Worth for an AI Assistant
In a system that assigns a 'worth' value to a response by taking the exponential of its reward score, doubling the reward score for a response will also double its assigned worth value.
Pros and Cons of Softmax Function
Softmax Regression (Activation)
Parameterized Softmax Layer
Plackett-Luce Selection Probability Formula
Conditional Probability Formula for Autoregressive Models using Softmax
A neural network's final layer produces the raw output scores (logits)
[2.0, 1.0, 0.1]for three possible classes. To convert these scores into class probabilities, a function is applied that first exponentiates each score and then normalizes these new values by dividing each by their sum. What is the resulting probability distribution? (Values are rounded to three decimal places).A function is used to convert a vector of raw, unnormalized scores
z = [z_1, z_2, ..., z_K]into a probability distribution. This function operates by first applying the standard exponential function to each score and then normalizing these new values by dividing each by their sum. If a constant valueCis added to every score in the input vectorz, resulting in a new vectorz' = [z_1+C, z_2+C, ..., z_K+C], how will the resulting output probability distribution be affected?Consider two input vectors of raw scores (logits) for a 3-class classification problem: Vector A =
[1, 2, 3]and Vector B =[1, 5, 10]. Both vectors are passed through a function that exponentiates each score and then normalizes the results by dividing by their sum. How will the resulting probability distribution for Vector B compare to the one for Vector A?You’re reviewing an internal evaluation script tha...
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Reconciling Training Log-Likelihood with Inference-Time Sequence Selection
Explaining a Counterintuitive Decoding Outcome Using Softmax, Next-Token Conditionals, and Sequence Log-Probability
Diagnosing a “High-Confidence Wrong Token” Bug in Autoregressive Scoring
Investigating a Production Scoring Bug: Softmax Normalization vs. Autoregressive Sequence Log-Probability
Design a Correct Sequence-Scoring Function for Autoregressive LLM Outputs
Root-Cause Analysis: Why a “More Likely” Token-by-Token Completion Loses on Total Sequence Score
Auditing a Candidate Completion Using Softmax Next-Token Probabilities and Autoregressive Log-Probability
Derivative of Softmax Cross-Entropy Loss with Respect to Logits
Numerical Overflow in Softmax Function
Learn After
A language model must choose the best response from a set of three options: A, B, and C. A reward function provides the following scores for each option: Option A has a score of 2.0, Option B has a score of 1.0, and Option C has a score of 0.5. Assuming the probability of selecting an option is calculated by normalizing its exponentiated reward score against the sum of all exponentiated scores, what is the approximate probability of the model selecting Option A?
Impact of Uniform Reward Shift on Selection Probabilities
Consider a model that selects a response from a set of options, where the probability of selecting any given response is proportional to the exponential of its reward score. If response Y has a reward score that is exactly twice the reward score of response Z, the model's probability of selecting Y will be exactly twice its probability of selecting Z.