positive-definite

Adjective

 * 1)  Said of a real, square matrix: that the product of it with a column vector on its right side and the transpose of that column vector on its left side is greater or equal to zero, only equaling zero if the vector itself is zero.
 * 2)  Said of a quadratic form: that the application of it to a tuple is greater or equal to zero, only equaling zero if the tuple itself is zero.