โ๏ธ Some examples
\(x\) or \(y\) โ a variable or value
\(\bar{x}\) โ the mean (average) of \(x\)
\(n\) โ number of observations
\(\sum\) โ summation: e.g \(\sum_{i=1}^n x_i\) means โadd all the \(x_i\) values from \(i = 1\) to \(n\)โ
\(x_i\) โ value of variable x for observation (row) i
\(x_{ij}\) โ value in row i, column j of a data matrix
\(\widehat{y}\) โ โy-hatโ = estimated or predicted value
\(\alpha, \beta, \gamma, \delta, \varepsilon\)โฆ โ Greek letters we assign meaning to
\(\mathbb{E}[X]\) โ expected value of \(X\)
\(f(x)\) โ a function of x (a rule that maps inputs to outputs)
\(y = a + b x\) โ a straight line