Pertemuan 1

library(ISLR)

library(matlib)

A <- matrix(3,5,2)
print(A)

##      [,1] [,2]
## [1,]    3    3
## [2,]    3    3
## [3,]    3    3
## [4,]    3    3
## [5,]    3    3

library(matlib)
M <- matrix(c(1,1,1,2,1,3,1,4),nrow=2,ncol=4)
A <- matrix(c(1,-2,-1,2,3,2,3,-2,1), nrow = 3, ncol = 3)
b <- c(6, -1, 2)

Smarket[2,]

##   Year  Lag1  Lag2   Lag3   Lag4   Lag5 Volume Today Direction
## 2 2001 0.959 0.381 -0.192 -2.624 -1.055 1.2965 1.032        Up

M2 <- rbind(Smarket[3,], Smarket[4,], Smarket[7,],
Smarket[9,], Smarket[10,])

dim(Smarket)

## [1] 1250    9

x <- 1:1250
plot(x, Smarket[,2],type="l")

library(matlib)
A <- matrix(c(1,2,1,1), nrow = 2, ncol = 2)
b <- c(4, 5)
Solve(A, b)

## x1    =  1 
##   x2  =  3

M <- matrix(c(1,0,1,0,1,0,0,1,0,1,1,0,0,1,0,1,475,489,542,422),
nrow=4,ncol=5)

a <- matrix(c(2,3,1,1,2,-5,-1,-2,4),nrow=3)
b <- c(1,1,3)

solve(a,b)

## [1] 1 2 3

solve(a)

##      [,1] [,2]          [,3]
## [1,]    2   -1  7.401487e-17
## [2,]   14   -9 -1.000000e+00
## [3,]   17  -11 -1.000000e+00

scale_row <- function(m, row, k){
 m[row, ] <- m[row, ]*k
 return(m)
}
(A <- matrix(1:15, nrow=5))

##      [,1] [,2] [,3]
## [1,]    1    6   11
## [2,]    2    7   12
## [3,]    3    8   13
## [4,]    4    9   14
## [5,]    5   10   15

scale_row(m=A, row=2, 10)

##      [,1] [,2] [,3]
## [1,]    1    6   11
## [2,]   20   70  120
## [3,]    3    8   13
## [4,]    4    9   14
## [5,]    5   10   15

replace_row <- function(m, row1, row2, k){
  m[row2, ] <- m[row2, ] + m[row1, ]*k
  return(m)
  replace_row(m=A, row1=1, row2=3, k=-3)
}

A <- matrix(c(1,-2,-1,2,3,2,3,-2,1), nrow = 3, ncol = 3)
b <- c(6, -1, 2)
Solve(A, b)

## x1      =  1 
##   x2    =  1 
##     x3  =  1

plotEqn3d(A,b, xlim=c(0,4), ylim=c(0,4))