Machine Learning
1. Related
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:
- \(\frac {d} {dx} \zeta(x) = \sigma(x)\)
- \(\frac {d} {dx} \sigma(x) = \sigma(x)(1- \sigma(x))\)
- \(\log \sigma(x) = - \zeta(-x)\)
- \(\zeta(x) - \zeta(-x) = x\)