Homogeneous least squares

In summary, the difference between minimizing y^{T}AA^{T}y and y^{T}AA^{+}y=y^{T}A(A^{T}A)^{-1}A^{T}y lies in the way the matrix A is decomposed. The first method uses a QR decomposition, while the second method uses properties related to the pseudo-inverse from a Singular Value Decomposition. Further details can be found by researching these methods.
  • #1
azay
19
0
Given a homogeneous linear least squares problem:
[tex]
A^{T}y=0
[/tex]

What is the difference between minimizing
[tex]
y^{T}AA^{T}y
[/tex] (the least square error)

and:

[tex]
y^{T}AA^{+}y=y^{T}A(A^{T}A)^{-1}A^{T}y
[/tex]

?

Thanks.
 
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  • #2
azay said:
Given a homogeneous linear least squares problem:
[tex]
A^{T}y=0
[/tex]

What is the difference between minimizing
[tex]
y^{T}AA^{T}y
[/tex] (the least square error)

and:

[tex]
y^{T}AA^{+}y=y^{T}A(A^{T}A)^{-1}A^{T}y
[/tex]

?

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.
 

Related to Homogeneous least squares

1. What is Homogeneous Least Squares?

Homogeneous least squares is a mathematical method used to find the best fitting line or curve for a set of data points. It is used to minimize the sum of the squared differences between the observed data and the predicted values.

2. How is Homogeneous Least Squares different from Ordinary Least Squares?

Homogeneous least squares is a special case of ordinary least squares, where the intercept term is forced to be zero. This means that the resulting line or curve will pass through the origin, while ordinary least squares allows for a non-zero intercept term.

3. What are the assumptions of Homogeneous Least Squares?

The main assumption of homogeneous least squares is that the errors in the data are normally distributed. Additionally, the data should be linearly related and the errors should be independent and have equal variances.

4. How is the best fitting line or curve determined in Homogeneous Least Squares?

The best fitting line or curve is determined by finding the coefficients that minimize the sum of the squared differences between the observed data and the predicted values. This is typically done using a mathematical technique called gradient descent.

5. In what fields is Homogeneous Least Squares commonly used?

Homogeneous least squares is commonly used in many fields, including statistics, machine learning, econometrics, and engineering. It is a fundamental tool for data analysis and is often used to model relationships between variables and make predictions.

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