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Log-sum-exp Function
easy

What is the relationship between the log-sum-exp function and the softmax function in the context of probability distributions?

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Choose the Best Answer

A

The softmax function is derived from the log-sum-exp function.

B

The log-sum-exp function is a specific case of the softmax function.

C

Both functions are identical in their outputs.

D

The log-sum-exp function cannot be used to compute probabilities.

Understanding the Answer

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Answer

The log‑sum‑exp (LSE) function is the logarithm of the normalizing constant that makes a set of unnormalized log‑probabilities into a proper probability distribution; it is written as log ∑ exp(zi). The softmax function takes those same log‑probabilities, exponentiates them, and divides each exponentiated value by the sum of all exponentials, which is exactly the denominator that the LSE computes. Thus, the softmax normalizes the scores into probabilities by using the LSE as the denominator, while the LSE itself can be used to compute the log‑partition function needed for many probabilistic models. For example, if we have scores z = [2, 0, −1], the softmax outputs exp(z)/∑exp(z) ≈ [0. 71, 0.

Detailed Explanation

Softmax turns raw scores into probabilities by dividing each exponential by the sum of all exponentials. Other options are incorrect because Some think log-sum-exp is a special case of softmax, but it is actually a helper that calculates the denominator; Softmax outputs a vector of probabilities, while log-sum-exp outputs a single number.

Key Concepts

softmax function
Topic

Log-sum-exp Function

Difficulty

easy level question

Cognitive Level

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