Last updated: 2019-01-25

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Rmd 7bbe37c John Blischak 2019-01-25 Add matrix addition and scalar multiplication.

Matrix addition and scalar multiplication

\[ A = \begin{bmatrix} -3 & -3 & 3 \\ 1 & 0 & 2 \\ 0 & -2 & 3 \end{bmatrix} \]

\[ B = \begin{bmatrix} -1 & 3 & 3 \\ -2 & 5 & 2 \\ 1 & 2 & 4 \end{bmatrix} \]

\[ C = \begin{bmatrix} -5 & 3 & 9 \\ -3 & 10 & 6 \\ 2 & 2 & 11 \end{bmatrix} \]

In R:

A <- matrix(c(-3, -3, 3,
              1, 0, 2,
              0, -2, 3),
            nrow = 3, byrow = TRUE)
B <- matrix(c(-1, 3, 3,
              -2, 5, 2,
              1, 2, 4),
            nrow = 3, byrow = TRUE)
C <- matrix(c(-5, 3, 9,
              -3, 10, 6,
              2, 2, 11),
            nrow = 3, byrow = TRUE)

Find \((A - B) + C\):

(A - B) + C
     [,1] [,2] [,3]
[1,]   -7   -3    9
[2,]    0    5    6
[3,]    1   -2   10

Find \(2A + B\):

2 * A + B
     [,1] [,2] [,3]
[1,]   -7   -3    9
[2,]    0    5    6
[3,]    1   -2   10

They are equal, therefore:

\[ 2A + B = (A - B) + C \]

\[ A + 2B -C = 0\]

A + 2 * B - C
     [,1] [,2] [,3]
[1,]    0    0    0
[2,]    0    0    0
[3,]    0    0    0


sessionInfo()
R version 3.5.2 (2018-12-20)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 18.04.1 LTS

Matrix products: default
BLAS: /usr/lib/x86_64-linux-gnu/atlas/libblas.so.3.10.3
LAPACK: /usr/lib/x86_64-linux-gnu/atlas/liblapack.so.3.10.3

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
 [1] workflowr_1.1.1.9001 Rcpp_1.0.0           digest_0.6.18       
 [4] rprojroot_1.2        backports_1.1.3      git2r_0.24.0        
 [7] magrittr_1.5         evaluate_0.12        stringi_1.2.4       
[10] fs_1.2.6             whisker_0.3-2        rmarkdown_1.11      
[13] tools_3.5.2          stringr_1.3.1        glue_1.3.0          
[16] xfun_0.4             yaml_2.2.0           compiler_3.5.2      
[19] htmltools_0.3.6      knitr_1.21