2020-11-28

Machine Learning

2. Useful Functions and Relations

  • Sigmoid
    • \(\sigma(x) = \frac 1 { 1 + \exp(-x)}\)
    • Range \((0,1)\)
    • Useful for producing probability for binomial distribution
  • Softplus
    • \(\zeta(x) = \log(1+\exp(x))\)
    • Range \((0, \infty)\)
    • A smooth version of positive-part function \(x^+ = max(0, x)\)
    • Useful for producing \(\beta\) or \(\sigma\) of normal distribution

Relations:

  • \(\frac {d} {dx} \zeta(x) = \sigma(x)\)
  • \(\frac {d} {dx} \sigma(x) = \sigma(x)(1- \sigma(x))\)
  • \(\log \sigma(x) = - \zeta(-x)\)
  • \(\zeta(x) - \zeta(-x) = x\)

References

Backlinks


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