A variable in a model that is adjusted during learning to improve performance.A parameter is a variable in a model that is adjusted during learning to improve performance. In machine learning, parameters are the internal coefficients that the model tunes to map inputs to outputs. For example, in a neural network, parameters are the weights and biases of connections between neurons. The process of learning involves iteratively updating these parameters to minimize the difference between predicted and actual outcomes.
The concept of adjustable parameters in models dates back to early statistics and least-squares fitting in the 19th century. In machine learning, the backpropagation algorithm, popularized in the 1980s, made it practical to tune millions of parameters in neural networks.
During training, the model makes predictions, compares them to known answers, and calculates an error. An optimization algorithm, such as gradient descent, then adjusts the parameters in the direction that reduces the error. This is repeated over many examples until the model performs well. The number of parameters can range from thousands in simple models to billions in large language models, and the way they are tuned determines the model's ability to generalize to new data.
Parameters are central to all machine learning systems, from image recognition and natural language processing to scientific models that predict molecular properties or discover new materials.
In physics, the 'no-hair theorem' for black holes is analogous to the idea that a model's behavior depends only on a few parameters (mass, charge, spin), not on the details of what fell in.
| J_{k\alpha} | variable | parameter being updated at iteration — parameter |
| \tau_\mu | variable | iteration step index — iteration index |
| \eta | variable | learning rate, step size — learning rate |
| \epsilon | variable | error or loss function — loss function |
| \frac{\partial}{\par | operator | computes the gradient of the error with respect to the parameter — partial derivative |





















