Least-squares solution of a linear inverse problem
= Least-squares solution of a linear inverse problem
= Least-squares solution
{synonym}
A <least-squares solution> minimizes $\|Ku-f\|$ over the source <Hilbert space>. It exists exactly when $f\in\mathcal R(K)\oplus\mathcal R(K)^\perp$, and then the solutions form a closed <affine subspace> with direction $\mathcal N(K)$.