and helpfully, in this context, if you're starting from the point of minimising the L2 error between the output of some linear function and a target, then the resulting linear system will have the form $A^T A x = A^T b$, so the matrix in question is $A^T A$, so it'll always be positive semidefinite.
and helpfully, in this context, if you're starting from the point of minimising the L2 error between the output of some linear function and a target, then the resulting linear system will have the form $A^T A x = A^T b$, so the matrix in question is $A^T A$, so it'll always be positive semidefinite.