Sum of squares
= Sum of squares
{title2=$\sum_i a_i^2$}
A sum of squares adds the <squares of numbers> $a_i^2$ for specified <real numbers> $a_i$. It is nonnegative and vanishes exactly when every term is zero. For the coordinates of a <vector>, it is the squared <Euclidean norm>; for <regression residuals>, it gives the <residual sum of squares> minimized by <ordinary least squares>.