Condition Number

If we have ${\sigma }_1\ge {\sigma }_2\ge \cdots \ge {\sigma }_n$ Then, $\text{condition number}=\frac{{\sigma }_1}{{\sigma }_n}$ Remember ${\sigma }_i=\sqrt{{\lambda }_i}$ where ${\lambda }_i$ is the eigenvalue of $A^{T}A$.