Formula

Conditional Log-Probability via Joint and Marginal Log-Probabilities

The conditional log-probability of an output sequence y given an input sequence x, denoted log Pr(y|x), can be calculated using the joint log-probability of the concatenated sequence [x, y] and the marginal log-probability of the input sequence x. The relationship is defined by the formula: logPr(yx)=logPr([x,y])logPr(x)\log \text{Pr}(\mathbf{y}|\mathbf{x}) = \log \text{Pr}([\mathbf{x}, \mathbf{y}]) - \log \text{Pr}(\mathbf{x}) This equation is derived by taking the logarithm of the standard definition of conditional probability, Pr(yx)=Pr([x,y])Pr(x)\text{Pr}(y|x) = \frac{\text{Pr}([x,y])}{\text{Pr}(x)}, and is crucial for connecting different probabilistic objectives in language modeling.

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Updated 2026-06-20

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Ch.5 Inference - Foundations of Large Language Models

Foundations of Large Language Models

Foundations of Large Language Models Course

Computing Sciences