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Lecture 6 Intersection of Hyperplanes and Matrix Inverse. Shang-Hua Teng. Expressing Elimination by Matrix Multiplication. Elementary or Elimination Matrix. The elementary or elimination matrix
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Lecture 6Intersection of Hyperplanes and Matrix Inverse Shang-Hua Teng
Elementary or Elimination Matrix • The elementary or elimination matrix That subtracts a multiple l of row j from row i can be obtained from the identity matrix I by adding (-l) in the i,j position
Pivot 1: The elimination of column 1 Elimination matrix
Inverse Matrices • In 1 dimension
Inverse Matrices • In high dimensions
Inverse Matrices • In 1 dimension • In higher dimensions
Inverses in Two Dimensions Proof:
Inverse and Linear System • Therefore, the inverse of A exists if and only if elimination produces n non-zero pivots (row exchanges allowed)
Inverse, Singular Matrix and Degeneracy Suppose there is a nonzero vector x such that Ax = 0[column vectors of A co-linear] then A cannot have an inverse Contradiction: So if A is invertible, then Ax =0 can only have the zero solution x=0
One More Property Proof So
Gauss-Jordan Elimination for Computing A-1 • 3D: Solving three linear equations defined by A simultaneously • n dimensions: Solving n linear equations defined by A simultaneously
Example:Gauss-Jordan Elimination for Computing A-1 • Make a Big Augmented Matrix