juniorCost Function
What is a cost function in machine learning?
Updated May 15, 2026
Short answer
A cost function measures how far model predictions are from actual values.
Deep explanation
A cost function (loss function) quantifies the error between predicted outputs and true labels. It guides optimization by providing a scalar value that the training process minimizes. Common examples include Mean Squared Error (MSE) for regression and Cross-Entropy for classification.
Real-world example
Used in housing price prediction to measure prediction error in dollars.
Common mistakes
- Confusing cost function with accuracy
- they represent opposite goals.
Follow-up questions
- Is cost function always differentiable?
- How does cost function affect training speed?