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Matrix Algebra Basics

Matrix Algebra Basics. Pam Perlich Urban Planning 5/6020. Algebra. Matrix. A matrix is any doubly subscripted array of elements arranged in rows and columns. Row Vector. [1 x n] matrix. Column Vector. [m x 1] matrix. Square Matrix. Same number of rows and columns. The Identity.

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Matrix Algebra Basics

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  1. Matrix Algebra Basics Pam Perlich Urban Planning 5/6020

  2. Algebra

  3. Matrix A matrix is any doubly subscripted array of elements arranged in rows and columns.

  4. Row Vector [1 x n] matrix

  5. Column Vector [m x 1] matrix

  6. Square Matrix Same number of rows and columns

  7. The Identity

  8. Identity Matrix Square matrix with ones on the diagonal and zeros elsewhere.

  9. Transpose Matrix Rows become columns and columns become rows

  10. Matrix Addition and Subtraction A new matrix C may be defined as the additive combination of matrices A and B where: C = A + B  is defined by: Note: all three matrices are of the same dimension

  11. Addition If and then

  12. Matrix Addition Example

  13. Matrix Subtraction C = A - B Is defined by

  14. Matrix Multiplication Matrices A and B have these dimensions: [r x c] and [s x d]

  15. Matrix Multiplication Matrices A and B can be multiplied if: [r x c] and [s x d] c = s

  16. Matrix Multiplication The resulting matrix will have the dimensions: [r x c] and [s x d] r x d

  17. Computation: A x B = C [2 x 2] [2 x 3] [2 x 3]

  18. Computation: A x B = C [3 x 2] [2 x 3] A and B can be multiplied [3 x 3]

  19. Computation: A x B = C [3 x 2] [2 x 3] Result is 3 x 3 [3 x 3]

  20. Inversion

  21. Matrix Inversion Like a reciprocal in scalar math Like the number one in scalar math

  22. Linear System of Simultaneous Equations First precinct: 6 arrests last week equally divided between felonies and misdemeanors. Second precinct: 9 arrests - there were twice as many felonies as the first precinct.

  23. Note: Inverse of is Solution Premultiply both sides by inverse matrix A square matrix multiplied by its inverse results in the identity matrix. A 2x2 identity matrix multiplied by the 2x1 matrix results in the original 2x1 matrix.

  24. General Form n equations in n variables: unknown values of x can be found using the inverse of matrix A such that

  25. Garin-Lowry Model The object is to find x given A and y . This is done by solving for x :

  26. Matrix Operations in Excel Select the cells in which the answer will appear

  27. Matrix Multiplication in Excel • Enter “=mmult(“ • Select the cells of the first matrix • Enter comma “,” • Select the cells of the second matrix • Enter “)”

  28. Matrix Multiplication in Excel Enter these three key strokes at the same time: control shift enter

  29. Matrix Inversion in Excel • Follow the same procedure • Select cells in which answer is to be displayed • Enter the formula: =minverse( • Select the cells containing the matrix to be inverted • Close parenthesis – type “)” • Press three keys: Control, shift, enter

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