Derivation of Cholesky Decomposition

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SUMMARY

The discussion focuses on the derivation of the Cholesky Decomposition for a 3x3 symmetric and semi-definite matrix. The key equation presented is S = L * L^t, where L is a lower-triangular matrix. Participants identified errors in the subscripts of the matrix components, specifically suggesting corrections to L_{32}, L_{21}, and L_{31} to ensure proper derivation. The conversation highlights the importance of accurate notation in understanding matrix decompositions.

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  • Understanding of matrix algebra, specifically symmetric and semi-definite matrices.
  • Familiarity with Cholesky Decomposition and its properties.
  • Knowledge of matrix multiplication and transposition.
  • Basic concepts of linear algebra, including lower-triangular matrices.
NEXT STEPS
  • Study the derivation process of Cholesky Decomposition in detail.
  • Learn about QR decomposition and its applications in linear algebra.
  • Explore numerical stability in matrix decompositions.
  • Investigate the use of Cholesky Decomposition in solving linear systems.
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Students and professionals in mathematics, engineering, and computer science who are studying linear algebra and matrix decompositions, particularly those focusing on Cholesky and QR methods.

BobTheLawyer
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Homework Statement


Derive Cholesky Decomposition for a 3x3 matrix

Homework Equations


IN: S is Real matrix with dimensions 3x3 and is Symmetric and semi-definite
Out: L is a Real matrix with dimensions 3x3 such that
  1. S=L*L^t
  2. L is lower-triangular

The Attempt at a Solution


We learned this in class, and here is what I have in my notes. Near the end, it starts not making sense, so I think I recorded something wrong, and I also don't fully get what's going on.

upload_2016-3-13_18-6-41.png
 

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You have miscopied the subscripts in the second last line. Replace ##L_{32}## by ##L_{33}##, ##L_{21}## by ##L_{22}## and ##L_{31}## by ##L_{32}## and then it will follow from the line above.
 
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andrewkirk said:
You have miscopied the subscripts in the second last line. Replace ##L_{32}## by ##L_{33}##, ##L_{21}## by ##L_{22}## and ##L_{31}## by ##L_{32}## and then it will follow from the line above.
Thank you so much! You're a life saver. This got me so confused. QR decomposition just clicked for me about 5 minutes ago, and now I get this too!
 

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