Homogeneous least squares

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SUMMARY

The discussion focuses on the differences between minimizing the least square error represented by the equation y^{T}AA^{T}y and minimizing y^{T}AA^{+}y, where A^{+} denotes the pseudo-inverse of matrix A. The first method utilizes QR decomposition, while the second relies on properties derived from Singular Value Decomposition (SVD). Understanding these distinctions is crucial for effectively solving homogeneous linear least squares problems.

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  • Understanding of homogeneous linear least squares problems
  • Familiarity with QR decomposition
  • Knowledge of Singular Value Decomposition (SVD)
  • Concept of pseudo-inverse in linear algebra
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azay
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Given a homogeneous linear least squares problem:
<br /> A^{T}y=0<br />

What is the difference between minimizing
<br /> y^{T}AA^{T}y<br /> (the least square error)

and:

<br /> y^{T}AA^{+}y=y^{T}A(A^{T}A)^{-1}A^{T}y<br />

?

Thanks.
 
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azay said:
Given a homogeneous linear least squares problem:
<br /> A^{T}y=0<br />

What is the difference between minimizing
<br /> y^{T}AA^{T}y<br /> (the least square error)

and:

<br /> y^{T}AA^{+}y=y^{T}A(A^{T}A)^{-1}A^{T}y<br />

?

Thanks.

Hey azay and welcome to the forums.

The difference has to do with how X is decomposed. The pseudo-inverse has the 'properties' that you would expect for an inverse but it's not the same.

According to this:

http://en.wikipedia.org/wiki/Linear_least_squares_(mathematics)#Computation

The first uses a QR decomposition, and the second uses properties related to the pseudo-inverse from a Singular Value Decomposition (SVD).

I am not exactly sure of the deep details myself, but I'm sure you can use the above link to answer more specific questions.
 

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