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Vocabulary

Understand the term. Connect the concept.

A practical dictionary of 512 AI, machine learning, mathematics, and programming terms from HerbDev’s AI Vocabulary app. Start with a definition, explore an example, then follow the concepts behind it.

Linked concepts open in a new tab. Audio reads the definition and example.

Sigmoid

Functions & Programming Concepts · Level 2 of 5

Sigmoid

A smooth S-shaped function commonly mapping real numbers into zero to one.

The logistic sigmoid is one common member and can saturate at extreme inputs.

Example

A binary classifier converts one logit into a probability.

Listen to the definition and example

Audio transcript

Sigmoid. A smooth S-shaped function commonly mapping real numbers into zero to one. The logistic sigmoid is one common member and can saturate at extreme inputs. For example: A binary classifier converts one logit into a probability.

Explore this concept

A useful analogy

A smooth dimmer that approaches its two limits without abruptly switching.

Why it matters

This helps you distinguish a computation’s contract, inputs, outputs, and behavior.

Technical detail

σ(x) = 1 / (1 + exp(−x)); σ′(x) = σ(x)(1 − σ(x)). The derivative becomes small at extreme inputs.

Common misconception

Sigmoid is not a hard threshold, and its output need not be a calibrated probability.

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Related concepts

Quick recall question

Try answering before looking back at the definition.

Put the terminology into context: How AI works · Machine-native representations · All learning paths

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