Linear-system residual norm
= Linear-system residual norm
{title2=$\|b-Ax\|$}
The <norm> of a <linear-system residual>, used to measure how closely an approximate solution satisfies its <linear system>. It differs from the solution-error norm $\|x_*-x\|$. Their relationship depends on the <matrix inverse> and the <condition number>, so a small residual alone is not a scale-free relative-error guarantee.