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How to multiply a matrix columns and rows with the same matrix rows and columns in R?
To multiply a rows or columns of a matrix, we need to use %*% symbol that perform the multiplication for matrices in R. If we have a matrix M with 5 rows and 5 columns then row 1 of M can be multiplied with column 1 of M using M[1,]%*%M[,1], similarly, we can multiply other rows and columns.
Example
M<−matrix(1:100,ncol=10) M
Output
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [1,] 1 11 21 31 41 51 61 71 81 91 [2,] 2 12 22 32 42 52 62 72 82 92 [3,] 3 13 23 33 43 53 63 73 83 93 [4,] 4 14 24 34 44 54 64 74 84 94 [5,] 5 15 25 35 45 55 65 75 85 95 [6,] 6 16 26 36 46 56 66 76 86 96 [7,] 7 17 27 37 47 57 67 77 87 97 [8,] 8 18 28 38 48 58 68 78 88 98 [9,] 9 19 29 39 49 59 69 79 89 99 [10,] 10 20 30 40 50 60 70 80 90 100 M[1,]%*%M[,1] [,1] [1,] 3355 M[1,]%*%M[,2] [,1] [1,] 7955 M[1,]%*%M[,3] [,1] [1,] 12555 M[1,]%*%M[,5] [,1] [1,] 21755 M[1,]%*%M[,7] [,1] [1,] 30955 M[1,]%*%M[,8] [,1] [1,] 35555 M[1,]%*%M[,10] [,1] [1,] 44755 M[2,]%*%M[,1] [,1] [1,] 3410 M[5,]%*%M[,3] [,1] [1,] 13575 M[9,]%*%M[,5] [,1] [1,] 25395 M[2,]%*%M[,10] [,1] [1,] 45710 M[3,]%*%M[,4] [,1] [1,] 17865 M[3,]%*%M[,6] [,1] [1,] 27465 M[3,]%*%M[,8] [,1] [1,] 37065 M[3,]%*%M[,10] [,1] [1,] 46665 M[4,]%*%M[,5] [,1] [1,] 23120 M[4,]%*%M[,8] [,1] [1,] 37820 M[4,]%*%M[,9] [,1] [1,] 42720 M[4,]%*%M[,10] [,1] [1,] 47620 M[5,]%*%M[,5] [,1] [1,] 23575 M[5,]%*%M[,8] [,1] [1,] 38575 M[5,]%*%M[,10] [,1] [1,] 48575 M[5,]%*%M[,1] [,1] [1,] 3575 M[6,]%*%M[,6] [,1] [1,] 29130 M[6,]%*%M[,10] [,1] [1,] 49530 M[6,]%*%M[,3] [,1] [1,] 13830 M[6,]%*%M[,1] [,1] [1,] 3630 M[7,]%*%M[,7] [,1] [1,] 34885 M[7,]%*%M[,10] [,1] [1,] 50485 M[7,]%*%M[,9] [,1] [1,] 45285 M[7,]%*%M[,2] [,1] [1,] 8885 M[8,]%*%M[,3] [,1] [1,] 14340 M[8,]%*%M[,4] [,1] [1,] 19640 M[8,]%*%M[,8] [,1] [1,] 40840 M[8,]%*%M[,10] [,1] [1,] 51440 M[,1]%*%M[9,] [,1] [1,] 3795 M[,1]%*%M[5,] [,1] [1,] 3575 M[,2]%*%M[5,] [,1] [1,] 8575 M[,4]%*%M[10,] [,1] [1,] 20350 M[,5]%*%M[9,] [,1] [1,] 25395
Updated on: 06-Nov-2020
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