ALGORITME & PEMROGRAMAN

Abdul Kudus, SSi., MSi., PhD.Senin, 6.30 – 9.00

Rabu, 10.00 – 12.00Rabu, 12.00 – 14.00

Membuat MatriksSalah satu cara membuat matriks adalah dengan perintah matrix().

> y <- matrix(c(1,2,3,4),nrow=2,ncol=2)> y[,1] [,2][1,] 1 3[2,] 2 4

Matriks dan Array

> y[,2][1] 3 4

Cara lain membuatnya adalah menyatakan unsur secara sendiri-sendiri> y <- matrix(nrow=2,ncol=2)> y[1,1] <- 1> y[2,1] <- 2> y[1,2] <- 3> y[2,2] <- 4

> y[,1] [,2][1,] 1 3[2,] 2 4

diisi kolom per kolom

Kita bisa mengisi baris per baris> m <- matrix(c(1,2,3,4,5,6),nrow=2,byrow=T)> m[,1] [,2] [,3][1,] 1 2 3[2,] 4 5 6

Operasi Matriks- Operasi Aljabar Lineir

> y %*% y # perkalian matriks[,1] [,2][1,] 7 15[2,]10 22

> 3*y # perkalian dengan skalar[,1] [,2][1,] 3 9[2,] 6 12> y+y # tambah[,1] [,2][1,] 2 6[2,] 4 8

- Pengindeksan (Subskrip) Matriks

> z[,1] [,2] [,3][1,] 1 1 1[2,] 2 1 0[3,] 3 0 1[4,] 4 0 0

> z[,2:3][,1] [,2][1,] 1 1[2,] 1 0[3,] 0 1[4,] 0 0

Ambil kolom ke-2 dan ke-3

> y[,1] [,2][1,]11 12[2,]21 22[3,]31 32

Memberi nilai kepada submatriks> y[,1] [,2][1,] 1 4[2,] 2 5[3,] 3 6> y[c(1,3),] <- matrix(c(1,1,8,12),nrow=2)> y[,1] [,2][1,] 1 8[2,] 2 5[3,] 1 12

> y[2:3,][,1] [,2][1,]21 22[2,]31 32> y[2:3,2][1] 22 32

> x <- matrix(nrow=3,ncol=3)> y <- matrix(c(4,5,2,3),nrow=2)> y[,1] [,2][1,] 4 2[2,] 5 3> x[2:3,2:3] <- y> x[,1] [,2] [,3][1,] NA NA NA[2,] NA 4 2[3,] NA 5 3

> y[,1] [,2][1,] 1 4[2,] 2 5[3,] 3 6> y[-2,][,1] [,2][1,] 1 4[2,] 3 6

buang baris ke-2

> library(pixmap)> logo <- read.pnm(system.file("pictures/logo.pgm", package="pixmap")[1])> logoPixmap image Type : pixmapGrey Size : 77x101 Resolution : 1x1 Bounding box : 0 0 101 77

Contoh: Mengedit Gambar

> plot(logo)

> str(logo)Formal class 'pixmapGrey' [package "pixmap"] with 6 slots ..@ grey : num [1:77, 1:101] 1 1 0.996 0.996 1 ... ..@ channels: chr "grey" ..@ size : int [1:2] 77 101 ..@ cellres : num [1:2] 1 1 ..@ bbox : num [1:4] 0 0 101 77 ..@ bbcent : logi FALSE

intensitas bernilai antara 0.0 (hitam) sampai 1.0 (putih).

Misal pixel pada baris 35, kolom 55 abu-abu

> logo@grey[35,55][1] 0.1960784

logo2 <- logologo2@grey[20:77,40:95] <- 0 #dihitamkanplot(logo2)

posisi gambar hurup R

bagian.blur <- function(gbr,rows,cols,q) { lrows <- length(rows) lcols <- length(cols) gbr.baru <- gbr blur <- matrix(nrow=lrows, ncol=lcols,runif(lrows*lcols)) gbr.baru @grey[rows,cols] <- (1-q)*gbr@grey[rows,cols] + q*blur return(gbr.baru)}

logo3 <- bagian.blur(logo,20:77,40:95,0.65)plot(logo3)

Membuat bagian huruf R di-blur

- Menyaring (Filtering) dalam Matriks

> x <- matrix(c(1:3,2:4),ncol=2)> xx[1,] 1 2[2,] 2 3[3,] 3 4> x[x[,2] >= 3,]x[1,] 2 3[2,] 3 4

Prosesnya

> j <- x[,2] >= 3> j[1] FALSE TRUE TRUE

Lalu gunakan utk menyaring> x[j,]x[1,] 2 3[2,] 3 4

> x[x[,2] >= 3,]x[1,] 2 3[2,] 3 4

Atau bisa langsung

> z <- c(5,12,13)> x[z %% 2 == 1,] [,1] [,2][1,] 1 2[2,] 3 4

Contoh lain

> m <- matrix(1:6,ncol=2)> m [,1] [,2][1,] 1 4[2,] 2 5[3,] 3 6> m[m[,1] > 1 & m[,2] > 5,][1] 3 6

Mengapa begini?

> M <- matrix(c(5,2,9,-1,10,11),ncol=2)> M [,1] [,2][1,] 5 -1[2,] 2 10[3,] 9 11> which(M > 2)[1] 1 3 5 6