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        | matrix -- ATA = AAT = I two vectors -- <u,v> = 0 functions -- ∫f(x)g(x)dx = 0 |  | 
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        | Idempotent and Orthogonal Matrix |  | 
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        | Existence/Uniqueness of Least Squares Solutions |  | Definition 
 
        | Always exist.  Unique when A is not rank deficient. |  | 
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        | ATAx = ATb where ATA is an mxm matrix.  Can solve with LU factorization. |  | 
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        | Ha = a - 2(vTa/vTv)v v = a - alpha(ek) alpha = -sign(ak)||ak|| where ak is a vector from position k on |  | 
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        | Orthogonal transformation to triangular form A=QR [image] |  | 
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        | Orthogonalize each successive vector against all the preceding ones. [image] |  | 
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        | As soon as each new vector qk is computed, immediately orthogonalize all remaining vectors against it... can use column pivoting [image] |  | 
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        | The rank of a matrix is equal to the number of nonzero singular values that it has |  | 
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        | A+ = VΣ+UT where the pseudo inverse of a scalar σ is 1/σ. |  | 
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        | Orthonormal Bases and SVD |  | Definition 
 
        | The columns of U corresponding to nonzero singular values form an orthonoral basis for span(A) and remaining columns of U form orthonoral basis for its orthogonal complement.  Columns of V corresponding to zero singular values form orthonormal basis for null space of A, and remaining columns of V form orthonormal basis for orthogonal complement of null space. |  | 
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