How Does Cholesky Factorization Demonstrate Matrix Norm Inequalities?

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Homework Statement


Let A =[A11 A12; A*12 A22] be Hermitian Positive-definite.
Use Cholesky factorizations
A11 = L1L*1
A22 = L2L*2
A22-A*12 A-111 A12 = L3L*3

to show the following:

||A22-A*12 A-111 A12||2≤||A||2

Homework Equations


The Attempt at a Solution



Using the submultiplicative and triangle inequalities:

||A22||2+||A*12||2 ||A-111||2||A12||2≤||A||2
 
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There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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