- #1
Drazick
- 10
- 2
Given a Positive Definite Matrix ## A \in {\mathbb{R}}^{2 \times 2} ## given by:
$$ A = \begin{bmatrix}
{A}_{11} & {A}_{12} \\
{A}_{12} & {A}_{22}
\end{bmatrix} $$
And a Matrix ## B ## Given by:
$$ B = \begin{bmatrix}
\frac{1}{\sqrt{{A}_{11}}} & 0 \\
0 & \frac{1}{\sqrt{{A}_{22}}}
\end{bmatrix} $$
Now, defining the Diagonal Scaling of ## A ## given by ## C = B A B ##.
One could see the main diagonal elements of ## C ## are all ## 1 ##.
Actually ## C ## is given by:
$$ C = B A B = \begin{bmatrix}
1 & \frac{{A}_{12}}{\sqrt{ {A}_{11} {A}_{22} }} \\
\frac{{A}_{12}}{\sqrt{ {A}_{11} {A}_{22} }} & 1
\end{bmatrix} $$
This scaling, intuitively, makes the Matrix closer to the identity Matrix (Smaller off diagonal values, 1 on the main diagonal) and hence improve the Condition Number.
Yet I couldn't prove it.
How could one prove ## \kappa \left( C \right) = \kappa \left( B A B \right) \leq \kappa \left( A \right) ##?
$$ A = \begin{bmatrix}
{A}_{11} & {A}_{12} \\
{A}_{12} & {A}_{22}
\end{bmatrix} $$
And a Matrix ## B ## Given by:
$$ B = \begin{bmatrix}
\frac{1}{\sqrt{{A}_{11}}} & 0 \\
0 & \frac{1}{\sqrt{{A}_{22}}}
\end{bmatrix} $$
Now, defining the Diagonal Scaling of ## A ## given by ## C = B A B ##.
One could see the main diagonal elements of ## C ## are all ## 1 ##.
Actually ## C ## is given by:
$$ C = B A B = \begin{bmatrix}
1 & \frac{{A}_{12}}{\sqrt{ {A}_{11} {A}_{22} }} \\
\frac{{A}_{12}}{\sqrt{ {A}_{11} {A}_{22} }} & 1
\end{bmatrix} $$
This scaling, intuitively, makes the Matrix closer to the identity Matrix (Smaller off diagonal values, 1 on the main diagonal) and hence improve the Condition Number.
Yet I couldn't prove it.
How could one prove ## \kappa \left( C \right) = \kappa \left( B A B \right) \leq \kappa \left( A \right) ##?