Gram matrix

The square matrix

consisting of pairwise scalar products of elements (vectors) of a (pre-)Hilbert space. All Gram matrices are non-negative definite. The matrix is positive definite if are linearly independent. The converse is also true: Any non-negative (positive) definite -matrix is a Gram matrix (with linearly independent defining vectors).

If are -dimensional vectors (columns) of an -dimensional Euclidean (Hermitian) space with the ordinary scalar product

then

where is the -matrix consisting of the columns . The symbol denotes the operation of matrix transposition, while the bar denotes complex conjugation of the variable. See also Gram determinant.

References

[a1]	H. Schwerdtfeger, "Introduction to linear algebra and the theory of matrices" , Noordhoff (1950) (Translated from German)