Negative log-likelihood is a loss function equal to the negative logarithm of a model’s likelihood. Minimizing it estimates parameters just as maximizing likelihood or log-likelihood does, while fitting naturally into machine-learning optimization workflows. section 2.3.4
Its practical role follows from how parameter estimation is performed:
- Use numerical optimization when no closed-form maximum-likelihood solution is available. section 2.3.4
- Fit neural-network parameters by seeking a candidate with relatively high likelihood, expressed as low negative log-likelihood. section 2.3.4
- Add regularization when optimization should discourage extreme parameter values; L2 regularization penalizes the sum of squared parameters. section 2.3.4






