library(ggplot2)
library(tsibble)
## Warning: package 'tsibble' was built under R version 4.3.1
## 
## Attaching package: 'tsibble'
## The following objects are masked from 'package:base':
## 
##     intersect, setdiff, union
library(tseries)
## Warning: package 'tseries' was built under R version 4.3.1
## Registered S3 method overwritten by 'quantmod':
##   method            from
##   as.zoo.data.frame zoo
library(MASS)
## Warning: package 'MASS' was built under R version 4.3.1
library(tseries)
library(forecast)
## Warning: package 'forecast' was built under R version 4.3.1
library(TTR)
## Warning: package 'TTR' was built under R version 4.3.1
library(TSA)
## Warning: package 'TSA' was built under R version 4.3.1
## Registered S3 methods overwritten by 'TSA':
##   method       from    
##   fitted.Arima forecast
##   plot.Arima   forecast
## 
## Attaching package: 'TSA'
## The following objects are masked from 'package:stats':
## 
##     acf, arima
## The following object is masked from 'package:utils':
## 
##     tar
library(imputeTS)
## Warning: package 'imputeTS' was built under R version 4.3.1
## 
## Attaching package: 'imputeTS'
## The following object is masked from 'package:tseries':
## 
##     na.remove
library(ggplot2)
library(lmtest)
## Loading required package: zoo
## 
## Attaching package: 'zoo'
## The following object is masked from 'package:imputeTS':
## 
##     na.locf
## The following object is masked from 'package:tsibble':
## 
##     index
## The following objects are masked from 'package:base':
## 
##     as.Date, as.Date.numeric
set.seed(1002)

IMPORT DATA

library(rio)
## Warning: package 'rio' was built under R version 4.3.1
data <- import ("https://raw.githubusercontent.com/divanm/mpdw/main/Data/DATA%20IDX%20COMPOSITE%20JKSE.csv")
x <- data$Open
y <- data$Close

Stasioner dalam Rataan dan Ragam

Pada dasarnya, pembangkitan data ARIMA akan menghasilkan data yang stasioner dalam rataan dan ragam karena akan mengikuti fungsi default-nya yang mengikuti pembangkitan bilangan acak normal dengan mean=0 dan ragam=1 .

Cek apakah ada missing value:

data[which(is.na(data$Close)),]
##           Date Open High Low Close Adj Close Volume
## 109 2022-05-02   NA   NA  NA    NA        NA     NA

Menduga missing value

data <- na_interpolation(data, option = "spline")
data
##           Date     Open     High      Low    Close Adj Close     Volume
## 1   2020-04-06 4623.429 4975.536 4562.902 4649.079  4649.079  255758500
## 2   2020-04-13 4649.079 4747.725 4480.607 4634.821  4634.821  218419900
## 3   2020-04-20 4634.821 4669.542 4441.090 4496.064  4496.064  238397200
## 4   2020-04-27 4496.064 4726.774 4474.893 4716.403  4716.403  183906700
## 5   2020-05-04 4716.403 4716.403 4576.228 4597.430  4597.430  179791700
## 6   2020-05-11 4597.430 4659.862 4460.273 4507.607  4507.607  231060000
## 7   2020-05-18 4507.607 4609.042 4487.179 4545.952  4545.952  139287000
## 8   2020-05-25 4545.952 4755.957 4541.834 4753.612  4753.612  288083800
## 9   2020-06-01 4753.612 5014.764 4753.612 4947.782  4947.782  372565600
## 10  2020-06-08 4947.782 5139.406 4712.073 4880.359  4880.359  490084700
## 11  2020-06-15 4880.359 5018.985 4809.619 4942.275  4942.275  336775500
## 12  2020-06-22 4942.275 4977.651 4879.133 4904.088  4904.088  260206800
## 13  2020-06-29 4904.088 4997.482 4862.041 4973.794  4973.794  249816600
## 14  2020-07-06 4973.794 5111.564 4973.490 5031.256  5031.256  358094500
## 15  2020-07-13 5031.256 5116.464 5024.934 5079.585  5079.585  349862400
## 16  2020-07-20 5079.585 5162.980 5031.888 5082.991  5082.991  427056800
## 17  2020-07-27 5082.991 5149.630 5080.121 5149.627  5149.627  356913600
## 18  2020-08-03 5149.627 5187.964 4928.468 5143.893  5143.893  423927900
## 19  2020-08-10 5157.834 5279.349 5157.834 5247.690  5247.690  340206700
## 20  2020-08-17 5247.690 5327.316 5243.995 5272.810  5272.810  188318800
## 21  2020-08-24 5272.810 5381.948 5261.408 5346.659  5346.659  665155800
## 22  2020-08-31 5346.659 5369.447 5188.609 5239.851  5239.851  568186400
## 23  2020-09-07 5235.010 5256.305 4754.799 5016.712  5016.712  492882200
## 24  2020-09-14 5060.024 5187.279 5013.186 5059.223  5059.223  503336800
## 25  2020-09-21 5058.990 5075.819 4820.331 4945.791  4945.791  406370800
## 26  2020-09-28 4962.953 4991.762 4841.362 4926.734  4926.734  440809400
## 27  2020-10-05 4947.040 5057.836 4915.685 5053.663  5053.663  421591900
## 28  2020-10-12 5078.129 5182.531 5064.171 5103.414  5103.414  525143900
## 29  2020-10-19 5116.758 5135.078 5063.697 5112.188  5112.188  522912300
## 30  2020-10-26 5113.149 5158.265 5110.618 5128.225  5128.225  210436500
## 31  2020-11-02 5108.029 5335.529 5073.500 5335.529  5335.529  516535700
## 32  2020-11-09 5371.971 5520.908 5319.420 5461.058  5461.058  669558400
## 33  2020-11-16 5500.034 5628.442 5462.460 5571.656  5571.656  789934400
## 34  2020-11-23 5583.330 5795.836 5583.330 5783.335  5783.335 1255563200
## 35  2020-11-30 5779.671 5853.156 5563.862 5810.483  5810.483 1160743700
## 36  2020-12-07 5854.303 6004.423 5854.303 5938.329  5938.329 1003237500
## 37  2020-12-14 5959.275 6160.977 5959.275 6104.324  6104.324 1292048600
## 38  2020-12-21 6131.623 6195.154 5853.261 6008.709  6008.709  692226400
## 39  2020-12-28 6067.000 6143.870 5962.010 5979.073  5979.073  526030000
## 40  2021-01-04 5997.830 6275.742 5929.048 6257.835  6257.835 1007037000
## 41  2021-01-11 6278.413 6472.312 6278.374 6373.412  6373.412 1527600500
## 42  2021-01-18 6365.026 6504.992 6283.313 6307.127  6307.127 1081229300
## 43  2021-01-25 6322.519 6322.727 5825.292 5862.352  5862.352  813369600
## 44  2021-02-01 5856.777 6179.368 5735.469 6151.729  6151.729  872980000
## 45  2021-02-08 6193.551 6286.291 6157.135 6222.521  6222.521  563483000
## 46  2021-02-15 6244.385 6314.555 6173.594 6231.932  6231.932  739117700
## 47  2021-02-22 6267.025 6312.873 6184.517 6241.796  6241.796  880483600
## 48  2021-03-01 6281.857 6394.452 6245.308 6258.749  6258.749  987879800
## 49  2021-03-08 6304.000 6364.357 6167.718 6358.209  6358.209  652024500
## 50  2021-03-15 6374.762 6387.736 6268.839 6356.160  6356.160  742809300
## 51  2021-03-22 6346.795 6354.939 6058.843 6195.562  6195.562  712370600
## 52  2021-03-29 6205.569 6230.990 5892.645 6011.456  6011.456  462735200
## 53  2021-04-05 6040.055 6113.156 5944.421 6070.209  6070.209  720785500
## 54  2021-04-12 6080.792 6115.620 5883.524 6086.258  6086.258  669695000
## 55  2021-04-19 6084.785 6096.995 5973.247 6016.864  6016.864  675194300
## 56  2021-04-26 6018.340 6033.900 5950.868 5995.616  5995.616  641211400
## 57  2021-05-03 5999.661 6005.088 5922.493 5928.309  5928.309  667078400
## 58  2021-05-10 5942.106 5985.372 5911.376 5938.351  5938.351  240955800
## 59  2021-05-17 5950.137 5958.793 5742.038 5773.120  5773.120  696962000
## 60  2021-05-24 5793.067 5904.838 5759.340 5848.616  5848.616  679387300
## 61  2021-05-31 5869.218 6103.859 5860.536 6065.166  6065.166  687508700
## 62  2021-06-07 6075.507 6134.882 5972.449 6095.497  6095.497 1116799300
## 63  2021-06-14 6110.797 6124.872 5944.053 6007.120  6007.120  955804200
## 64  2021-06-21 5959.965 6130.096 5884.918 6022.399  6022.399  851733600
## 65  2021-06-28 6015.279 6043.432 5913.591 6023.008  6023.008  825550700
## 66  2021-07-05 6024.165 6080.222 5985.354 6039.844  6039.844  754205300
## 67  2021-07-12 6060.054 6114.286 5947.618 6072.510  6072.510  716924100
## 68  2021-07-19 6062.966 6166.305 6015.149 6101.690  6101.690  597748400
## 69  2021-07-26 6109.031 6160.463 6068.512 6070.039  6070.039  869133600
## 70  2021-08-02 6098.008 6263.539 6048.101 6203.431  6203.431 1228093800
## 71  2021-08-09 6203.747 6239.015 6042.475 6139.492  6139.492  869347300
## 72  2021-08-16 6144.943 6147.304 5938.407 6030.772  6030.772  796085900
## 73  2021-08-23 6037.700 6138.497 6021.954 6041.366  6041.366  977033500
## 74  2021-08-30 6062.113 6169.056 6054.281 6126.921  6126.921  893890700
## 75  2021-09-06 6137.126 6150.358 5982.766 6094.873  6094.873  958513400
## 76  2021-09-13 6080.062 6137.669 6052.970 6133.246  6133.246  992844400
## 77  2021-09-20 6132.034 6163.884 5996.407 6144.815  6144.815  950159400
## 78  2021-09-27 6141.470 6286.943 6086.263 6228.845  6228.845 1102928200
## 79  2021-10-04 6234.799 6497.656 6234.799 6481.769  6481.769 1172175100
## 80  2021-10-11 6482.957 6680.009 6451.678 6633.338  6633.338  941178200
## 81  2021-10-18 6649.281 6687.134 6585.557 6643.738  6643.738  757917300
## 82  2021-10-25 6626.367 6680.117 6509.878 6591.346  6591.346  899190300
## 83  2021-11-01 6618.122 6627.851 6480.010 6581.785  6581.785  828841100
## 84  2021-11-08 6599.405 6714.158 6592.055 6651.054  6651.054  921099300
## 85  2021-11-15 6661.849 6720.988 6592.228 6720.263  6720.263 1134263700
## 86  2021-11-22 6731.515 6754.464 6544.896 6561.553  6561.553 1087199900
## 87  2021-11-29 6552.803 6647.477 6484.578 6538.506  6538.506  795330100
## 88  2021-12-06 6552.816 6652.922 6525.985 6652.922  6652.922 1078695000
## 89  2021-12-13 6663.739 6688.379 6559.303 6601.932  6601.932 1011838100
## 90  2021-12-20 6571.345 6592.167 6529.593 6562.900  6562.900  941359400
## 91  2021-12-27 6570.558 6621.579 6562.554 6581.482  6581.482  763376600
## 92  2022-01-03 6586.260 6738.110 6586.133 6701.316  6701.316  884588500
## 93  2022-01-10 6697.376 6727.767 6625.757 6693.401  6693.401  854569300
## 94  2022-01-17 6711.406 6726.373 6534.270 6726.373  6726.373  805658500
## 95  2022-01-24 6700.822 6712.262 6523.929 6645.511  6645.511  986322200
## 96  2022-01-31 6656.707 6731.391 6626.656 6731.391  6731.391  777116900
## 97  2022-02-07 6751.349 6874.351 6748.909 6815.607  6815.607 1238259600
## 98  2022-02-14 6791.316 6899.410 6698.509 6892.818  6892.818 1092845600
## 99  2022-02-21 6896.752 6929.911 6758.861 6888.171  6888.171 1127214800
## 100 2022-02-28 6964.697 6996.935 6861.959 6928.328  6928.328  769293800
## 101 2022-03-07 6905.324 6929.863 6814.183 6922.602  6922.602 1085654100
## 102 2022-03-14 6949.206 7032.702 6894.921 6954.965  6954.965  949839000
## 103 2022-03-21 6945.893 7055.341 6929.934 7002.532  7002.532 1086012100
## 104 2022-03-28 6996.318 7099.497 6987.223 7078.760  7078.760  890142300
## 105 2022-04-04 7082.247 7216.494 7060.214 7210.835  7210.835  986772300
## 106 2022-04-11 7212.003 7355.300 7146.586 7235.532  7235.532 1073108900
## 107 2022-04-18 7245.504 7297.394 7174.810 7225.606  7225.606 1118782600
## 108 2022-04-25 7204.161 7267.112 7121.860 7228.914  7228.914  805992800
## 109 2022-05-02 7324.780 7258.343 6799.028 6840.217  6840.217  697324161
## 110 2022-05-09 7154.917 7156.484 6509.879 6597.993  6597.993  778348200
## 111 2022-05-16 6603.893 6965.106 6574.136 6918.144  6918.144  816107000
## 112 2022-05-23 6930.939 7032.822 6802.713 7026.256  7026.256  750357000
## 113 2022-05-30 7052.173 7233.995 6974.616 7182.961  7182.961  949041500
## 114 2022-06-06 7163.174 7257.997 7051.223 7086.648  7086.648 1281571500
## 115 2022-06-13 6992.230 7138.496 6882.644 6936.967  6936.967 1322143900
## 116 2022-06-20 6937.008 7067.747 6859.599 7042.937  7042.937 1133599100
## 117 2022-06-27 7043.018 7070.519 6777.317 6794.328  6794.328  840889500
## 118 2022-07-04 6794.368 6796.519 6559.637 6740.219  6740.219  810131700
## 119 2022-07-11 6740.019 6757.087 6607.702 6651.905  6651.905  794121300
## 120 2022-07-18 6652.065 6901.720 6611.926 6886.962  6886.962  853012300
## 121 2022-07-25 6887.042 7032.353 6857.801 6951.123  6951.123 1387470600
## 122 2022-08-01 6951.123 7090.767 6902.630 7084.655  7084.655 1102623400
## 123 2022-08-08 7084.655 7181.100 7021.673 7129.277  7129.277 1169007600
## 124 2022-08-15 7129.277 7230.111 7080.753 7172.434  7172.434  931624200
## 125 2022-08-22 7172.434 7210.163 7064.501 7135.248  7135.248 1241361100
## 126 2022-08-29 7135.088 7223.126 7015.347 7177.179  7177.179 1359158600
## 127 2022-09-05 7177.139 7287.700 7147.976 7242.656  7242.656 1535050500
## 128 2022-09-12 7242.696 7377.495 7163.073 7168.870  7168.870 1462367300
## 129 2022-09-19 7168.950 7252.186 7127.457 7178.583  7178.583 1266925400
## 130 2022-09-26 7178.503 7178.503 6926.860 7040.798  7040.798 1036700200
## 131 2022-10-03 7040.798 7135.908 6995.062 7026.783  7026.783 1020558200
## 132 2022-10-10 7026.663 7026.663 6814.530 6814.530  6814.530 1046699200
## 133 2022-10-17 6814.530 7058.911 6747.380 7017.771  7017.771  995211200
## 134 2022-10-24 7017.811 7108.816 7016.702 7056.040  7056.040  989950000
## 135 2022-10-31 7056.040 7128.136 6962.853 7045.527  7045.527  907843500
## 136 2022-11-07 7045.527 7111.440 6956.288 7089.206  7089.206  989493100
## 137 2022-11-14 7089.206 7104.764 6955.529 7082.181  7082.181  831349300
## 138 2022-11-21 7082.181 7108.831 7013.221 7053.150  7053.150  816522900
## 139 2022-11-28 7053.110 7090.277 6967.950 7019.639  7019.639  932257000
## 140 2022-12-05 7019.639 7053.903 6683.629 6715.118  6715.118  763168800
## 141 2022-12-12 6715.118 6854.098 6641.810 6812.193  6812.193 1047258100
## 142 2022-12-19 6812.154 6844.121 6715.045 6800.673  6800.673  668236600
## 143 2022-12-26 6800.713 6858.147 6796.167 6835.808  6835.808  117543200
data[109,]
##           Date    Open     High      Low    Close Adj Close    Volume
## 109 2022-05-02 7324.78 7258.343 6799.028 6840.217  6840.217 697324161
stas <- ts(data$Close)

Plot Time Series

plot_stas <- stas |> as_tsibble() |> 
  ggplot(aes(x = index, y = value)) + geom_line() + theme_bw() +
  xlab("Obs") + ylab("Nilai")
plot_stas

mean(stas)
## [1] 6200.346

Plot deret waktu di atas menunjukkan bahwa data tidak stasioner dalam rataan, ditandai dengan data yang memiliki pola tren.

Plot ACF

acf(stas)

Berdasarkan plot ACF, terlihat bahwa plot ACF pada data tersebut cenderung tails off slowlysehingga berdasarkan plot ACF data tidak stasioner.

Uji ADF

tseries::adf.test(stas)
## 
##  Augmented Dickey-Fuller Test
## 
## data:  stas
## Dickey-Fuller = -2.291, Lag order = 5, p-value = 0.4553
## alternative hypothesis: stationary

\(H_0\) : Data tidak stasioner dalam rataan

\(H_1\) : Data stasioner dalam rataan

Berdasarkan uji ADF tersebut, didapat p-value sebesar 0.4553 yang lebih besar dari taraf nyata 5% sehingga tak tolak \(H_0\) dan menandakan bahwa data tidak stasioner dalam rataan. Hal ini sesuai dengan hasil eksplorasi menggunakan plot time series dan plot ACF.

Plot Box-Cox

index <- seq(1:143)
bc = boxcox(stas~index, lambda = seq(-2,10,by=0.01))

#Nilai Rounded Lambda
lambda <- bc$x[which.max(bc$y)]
lambda
## [1] 3.49
#SK
bc$x[bc$y > max(bc$y) - 1/2 * qchisq(.95,1)]
##   [1] 2.67 2.68 2.69 2.70 2.71 2.72 2.73 2.74 2.75 2.76 2.77 2.78 2.79 2.80 2.81
##  [16] 2.82 2.83 2.84 2.85 2.86 2.87 2.88 2.89 2.90 2.91 2.92 2.93 2.94 2.95 2.96
##  [31] 2.97 2.98 2.99 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11
##  [46] 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21 3.22 3.23 3.24 3.25 3.26
##  [61] 3.27 3.28 3.29 3.30 3.31 3.32 3.33 3.34 3.35 3.36 3.37 3.38 3.39 3.40 3.41
##  [76] 3.42 3.43 3.44 3.45 3.46 3.47 3.48 3.49 3.50 3.51 3.52 3.53 3.54 3.55 3.56
##  [91] 3.57 3.58 3.59 3.60 3.61 3.62 3.63 3.64 3.65 3.66 3.67 3.68 3.69 3.70 3.71
## [106] 3.72 3.73 3.74 3.75 3.76 3.77 3.78 3.79 3.80 3.81 3.82 3.83 3.84 3.85 3.86
## [121] 3.87 3.88 3.89 3.90 3.91 3.92 3.93 3.94 3.95 3.96 3.97 3.98 3.99 4.00 4.01
## [136] 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 4.15 4.16
## [151] 4.17 4.18 4.19 4.20 4.21 4.22 4.23 4.24 4.25 4.26 4.27 4.28 4.29 4.30 4.31
## [166] 4.32

Gambar di atas menunjukkan nilai rounded value (\(\lambda\)) optimum sebesar 3,49 dan pada selang kepercayaan 95% nilai memiliki batas bawah 2.67 dan batas atas 4,00. Selang tersebut tidak memuat nilai satu sehingga dapat dikatakan bahwa data tidak stasioner dalam ragam.

Partisi Data

Bagian 1

dt_stas1 <- stas[1:90] |> ts()
mean(dt_stas1)
## [1] 5753.671
var(dt_stas1)
## [1] 402891.1

Plot Time Series

dt_stas1 |> as_tsibble() |> 
  ggplot(aes(x = index, y = value)) +
  geom_line() + theme_bw() +
  xlab("Obs") + ylab("Nilai")

Plot deret waktu di atas menunjukkan bahwa data tidak stasioner dalam rataan, ditandai dengan data berpola tren naik.

Plot ACF

acf(dt_stas1)

Berdasarkan plot ACF, terlihat bahwa plot ACF pada data tersebut cenderung tails off slowly sehingga berdasarkan plot ACF data tidak stasioner. #### Uji ADF

tseries::adf.test(dt_stas1)
## 
##  Augmented Dickey-Fuller Test
## 
## data:  dt_stas1
## Dickey-Fuller = -2.3111, Lag order = 4, p-value = 0.4481
## alternative hypothesis: stationary

\(H_0\) : Data tidak stasioner dalam rataan

\(H_1\) : Data stasioner dalam rataan

Berdasarkan uji ADF tersebut, didapat p-value sebesar 0.4481 yang lebih besar dari taraf nyata 5% sehingga tak tolak \(H_0\) dan menandakan bahwa data tidak stasioner dalam rataan. Hal ini sesuai dengan hasil eksplorasi menggunakan plot time series dan plot ACF.

Plot Boxcox

index <- seq(1:90)
bc = boxcox(dt_stas1~index, lambda = seq(-4,10,by=1))

#Nilai Rounded Lambda
lambda <- bc$x[which.max(bc$y)]
lambda
## [1] 2.787879
#SK
bc$x[bc$y > max(bc$y) - 1/2 * qchisq(.95,1)]
##  [1] 1.373737 1.515152 1.656566 1.797980 1.939394 2.080808 2.222222 2.363636
##  [9] 2.505051 2.646465 2.787879 2.929293 3.070707 3.212121 3.353535 3.494949
## [17] 3.636364 3.777778 3.919192 4.060606 4.202020

Gambar di atas menunjukkan nilai rounded value (\(\lambda\)) optimum sebesar 2.787879 dan pada selang kepercayaan 95% nilai memiliki batas bawah 1.373737 dan batas atas 4.202020. Selang tersebuttidak memuat nilai satu sehingga dapat dikatakan bahwa data tidak stasioner dalam ragam.

Bagian 2

dt_stas2 <- stas[1:130] |> ts()
mean(dt_stas2)
## [1] 6125.238
var(dt_stas2)
## [1] 603129.4

Plot Time Series

dt_stas2 |> as_tsibble() |> 
  ggplot(aes(x = index, y = value)) +
  geom_line() + theme_bw() +
  xlab("Obs") + ylab("Nilai")

Plot deret waktu di atas menunjukkan bahwa data tidak stasioner dalam rataan, ditandai dengan data yang berpola tren naik.

Plot ACF

acf(dt_stas2)

Berdasarkan plot ACF, terlihat bahwa plot ACF pada data tersebut cenderung tails off slowly

Uji ADF

adf.test(dt_stas2)
## 
##  Augmented Dickey-Fuller Test
## 
## data:  dt_stas2
## Dickey-Fuller = -2.8358, Lag order = 5, p-value = 0.229
## alternative hypothesis: stationary

\(H_0\) : Data tidak stasioner dalam rataan

\(H_1\) : Data stasioner dalam rataan

Berdasarkan uji ADF tersebut, didapat p-value sebesar 0.229 yang lebih besar dari taraf nyata 5% sehingga tak tolak \(H_0\) dan menandakan bahwa data tidak stasioner dalam rataan. Hal ini sesuai dengan hasil eksplorasi menggunakan plot time series dan plot ACF.

Plot Boxcox

index <- seq(1:130)
bc = boxcox(dt_stas2~index, lambda = seq(-5,12,by=1))

#Nilai Rounded Lambda
lambda <- bc$x[which.max(bc$y)]
lambda
## [1] 3.070707
#SK
bc$x[bc$y > max(bc$y) - 1/2 * qchisq(.95,1)]
## [1] 2.383838 2.555556 2.727273 2.898990 3.070707 3.242424 3.414141 3.585859
## [9] 3.757576

Gambar di atas menunjukkan nilai rounded value (\(\lambda\)) optimum sebesar 3.070707 dan pada selang kepercayaan 95% nilai memiliki batas bawah 2.383838 dan batas atas 3.757576. Selang tersebut tidak memuat nilai satu sehingga dapat dikatakan bahwa data tidak stasioner dalam ragam.