Sum of squares
In mathematics, statistics and elsewhere, sums of squares occur in a number of contexts:
- Statistics
- For partitioning of variance, see Partition of sums of squares
- For the "sum of squared deviations", see Least squares
- For the "sum of squared differences", see Mean squared error
- For the "sum of squared error", see Residual sum of squares
- For the "sum of squares due to lack of fit", see Lack-of-fit sum of squares
- For sums of squares relating to model predictions, see Explained sum of squares
- For sums of squares relating to observations, see Total sum of squares
- For sums of squared deviations, see Squared deviations
- For modelling involving sums of squares, see Analysis of variance
- For modelling involving the multivariate generalisation of sums of squares, see Multivariate analysis of variance
- Number theory
- Algebra and algebraic geometry
- For representing a polynomial as the sum of squares of polynomials, see Polynomial SOS.
- For representing a multivariate polynomial that takes only non-negative values over the reals as a sum of squares of rational functions, see Hilbert's seventeenth problem.
- The Brahmagupta–Fibonacci identity says the set of all sums of two squares is closed under multiplication.
- Euclidean geometry and other inner-product spaces
- The Pythagorean theorem says that the square on the hypotenuse of a right triangle is equal in area to the sum of the squares on the legs