The [[Gram Matrix]] of some [[Matrix]] $A$ is the [[Matrix Product|product]] of $A$ with its [[Matrix Transpose|Transpose]]. $\huge G_{A} = A A^{\intercal} $ This can also be expressed as the [[Outer Product]] between $A$ and itself. $ \huge G_{A} = A\otimes A $ If the [[Gram Matrix]] is a [[Matrix|Square Matrix]], it will *always* be [[Symmetric Matrix|Symmetric]]. If $A$ is [[Injective]], then the [[Gram Matrix]] is [[Positive Semidefininite]].