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Consider the set of inconsistent linear equations Ax = b

given by

[1 0] [x1] = [1]
[0 1] [x2] = [1]
[1 1] = [0]

Find the "hat" matrix H. Using Matlab, numerically verify H =
H2. Argue why.

1 Answer

4 votes

Final answer:

The question is about finding the hat matrix H for a set of inconsistent linear equations and verifying that H is idempotent (H = H^2) using Matlab. Since A is not specified, we cannot calculate H directly, but the hat matrix is generally given by H = A(A^TA)^-1A^T.

Step-by-step explanation:

The student is asking how to find the "hat" matrix H for a set of inconsistent linear equations and to verify numerically that H = H^2 using Matlab, which indicates that H is an idempotent matrix. The hat matrix, also known as the projection matrix, maps the vector of observations to the vector of predicted values in linear regression. Although the student provided information on vectors in a rectangular coordinate system and the properties of vectors, this information doesn't directly help in finding the hat matrix for the given linear equations:

  • [1 0] [x1] = [1]
  • [0 1] [x2] = [1]
  • [1 1] [x1 x2]T = [0]

In this scenario, the matrix A is not provided; however, the concept of the hat matrix in the context of linear algebra typically involves the matrix A and its transpose. Once the matrix A is known, the hat matrix is calculated as H = A(ATA)-1AT. To numerically verify that H = H^2, you would perform a matrix multiplication of H with itself in Matlab and show that the result is equal to H.

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