Reduce P = A(ATA)-1AT to P = BBT

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SUMMARY

The discussion focuses on the mathematical reduction of the expression P = A(ATA)-1AT to P = BBT, specifically when the column vectors of matrix A form an orthonormal set. It is established that if the columns of A are orthonormal, then A^T A equals the identity matrix I, which has a rank equal to the number of columns in A. The proof involves manipulating the product in block form to demonstrate this equivalence clearly.

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  • Understanding of matrix algebra, specifically matrix multiplication and transposition.
  • Familiarity with orthonormal sets and their properties in linear algebra.
  • Knowledge of the identity matrix and its role in matrix equations.
  • Ability to manipulate block matrices and perform matrix reductions.
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squenshl
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How do I reduce P = A(ATA)-1AT to P = BBT whenever the column vectors of A form an orthonormal set.
 
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If the columns are an orthonormal set, then A^T A == I (where I has rank of the number of columns). The proof is mainly writing out that product in block form.
 

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