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Unformatted text preview: Math 18.02 (Spring 2009): Lecture 3 Matrices. Inverse Matrices February 6 Reading Material: From Course Notes M. Last time: Cross product and determinant Today: Matrices and Inverse Matrices Recall: A matrix A is defined as A = a 11 a 12 a 1 n . . . a m 1 a m 2 a mn = ( a i,j ) n = # columns and m = # rows hence A is a m n matrix. 2 Matrix Arithmetic Addition: If A, B are m n matrices then A + B is obtained by adding entries in the same location . Multiplication by scalar: Given a matrix A = ( a ij ) and a scalar c we define the new matrix cA as cA = ( ca ij ) , This means that we have to multiply every entry of A by the scalar c . 1 Mutiplication of two matrices: If A is a m n and B is a n s matrix then A B is a m s matrix such that its c ij entry is given by ( a i 1 a i 2 a in ) b 1 j b 2 j . . . b nj = c ij i = 1 , . . . , m j = 1 , . . . , s c ij = row i col j = n X k =1 a ik b kj dot product so A ( m n ) times...
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- Spring '08