Proof Hat Matrix Is Symmetric
In locally weighted scatterplot smoothing LOESS for example the hat matrix is in general neither symmetric.
Proof hat matrix is symmetric. We can show that both H and I H are orthogonal projections. This is denoted A 0 where here 0 denotes the zero matrix. Any symmetric matrix 1 has only real eigenvalues.
Thus AB T A T B T. But A and B are symmetric. 1A square matrix A is a projection if it is idempotent 2A projection A is orthogonal if it is also symmetric.
From the Theorem 1 we know that A A is a symmetric matrix and A A is a skew-symmetric matrix. Equivalently a square matrix is symmetric if and only if there exists anorthogonal matrixSsuchthatSTASis diagonal. A good way to tell if a matrix is positive deļ¬nite is to check that all its pivots are positive.
Any Square matrix can be expressed as the sum of a symmetric and a skew-symmetric matrix. The symmetric matrix should be a square matrix. 1 Let 2 C be an eigenvalue of the symmetric matrix A.
Along the way I present the proo. This means AB T AB. However this is not always the case.
11 Positive semi-de nite matrices De nition 3 Let Abe any d dsymmetric matrix. Some of the symmetric matrix properties are given below. The product of two symmetric matrices is usually not symmetric.