Definition
Plain language
A mathematical curve that smoothly squishes any number into a value between zero and one.
As stated in the literature
A logistic activation function mapping reals to (0,1), commonly used as a gating function in neural networks.
Why it matters: It's the standard way to compress unbounded scores into probabilities or gate values, and shows up everywhere from classifiers to mixture-of-experts routers.
For example, a sigmoid turns a raw score of -3 into about 0.05 and a score of +3 into about 0.95, which can be read as probabilities.
Heard on the show
“And there's a sigmoid gate on the weighting that's worth flagging — a neighbor only really contributes if it was both similar AND successful.”Episode 042 — An Agentic Scientific Computing System That Actually Remembers What It Learns