Relative condition number, Ill conditioned, Well conditioned

664 Views Asked by At

I'm currently learning about relative condition number (K), and how they are considered as well conditioned or ill conditioned.

From my understanding, a large K value represents ill-conditioned, while a small K value represents well-conditioned.

However, is there a range where K can be labeled as large(ill) or small(well)?

For example, $x^3$ would give a value of $K = 3$ and $x^{1/3}$ would give a value of $K = \frac{1}{3}$. But it doesn't give me the idea if K is large or small, hence I am unable to tell if they are well-conditioned or ill-conditioned.

My apologies for the poor formatting as I am still quite new here.

1

There are 1 best solutions below

0
On

Well the post is 4 years old but I think it deserves an answer. Probably the author has found the solution.

If we mean this condition number where $k(A)=\|A\|\|A^{-1}\|$ and $A$ is a matrix, then a large k value means that the matrix is ill-conditioned. This means that if a small change is made in its elements (as it happens when we put data in the computer to make calculations) the solution of the system might differ a lot from the real solution. Thus it can be proved that $k(A)\geq 1$ so I am not sure if the number in the question is the one I am reffering to. As I was tought, a condition number of order larger than $10^5$ is bad (and the matrix is ill-conditioned). A condition number of order (approximately) $1-10^2$ is good (so the matrix is well-conditioned). The range $10^3-10^4$ is something between the two cases (well and ill).