Gram product
= Gram product
{title2=$T^\top T\text{ or }TT^\top$}
A real <matrix> product giving pairwise <dot products> of columns, for $T^\top T$, or rows, for $TT^\top$. It is a <positive semidefinite matrix>. The <kernel of a Gram product> is determined by the corresponding factor, which makes these products useful for converting a zero <quadratic form> into an exact <null space> condition.