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SESK: Stuff Everyone Should Know · sesk.info/ai-sigmoid-range

Into what open interval does the logistic sigmoid map real inputs?

Its output lies between 0 and 1.

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  1. Negative infinity to infinity
  2. 0 to 1 ✔
  3. -1 to 1

Why: The logistic sigmoid is 1 divided by (1 plus e to the power negative x). It approaches 0 and 1 but never reaches either for finite x.

Huh, didn't know that: At an input of zero, the logistic sigmoid equals exactly 0.5.

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Sigmoid never reaches one, but it keeps approaching the subject.
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References

Answer: 0 to 1. The logistic sigmoid is 1 divided by (1 plus e to the power negative x). It approaches 0 and 1 but never reaches either for finite x.

  1. Google Machine Learning Crash Course: Activation functions developers.google.com/machine-learning/crash-course/neural-networks/activation-functions
    producing an output value between 0 and 1
    Checked 2026-10-10.

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