Judul: Peramalan Harga Emas Menggunakan Metode Bagging Pemulusan Eksponensial
Abstrak: Gold is one of the precious metals that remain popular among investors nowadays. It provides investors a safe haven when the economy is questionable. It is crucial to provide better information about the prospect of gold prices before investing. One way to do it in the statistical realm is through forecasting using the exponential smoothing method. In order to tackle challenges that may be encountered, an additional approach called bootstrap aggregating (bagging) was proposed. This study aims to compare the performance of exponential smoothing in a condition with and without bagging. Data that were used are gold prices from January 4th, 2010 until February 27th, 2022. As there is only sign of a trend component, it can be modelled using the Holt’s linear and the additive damped trend method. Models were evaluated based on MAPE and RMSE. Based on Wilcoxon signed-rank test, adding bagging is proven to bring statistically proven difference. For the daily and weekly series, the best model is Holt’s linear smoothing with bagging. While for the monthly series, the best one is Holt’s Linear smoothing without bagging. Lastly, it is predicted that gold prices will keep increasing until reaching more than Rp1000000/g in February 2023., Emas merupakan salah satu logam mulia yang popular di kalangan investor. Emas dapat menjadi alternatif investasi yang aman ketika kondisi perekonomian sedang lesu. Tentu peramalan harga emas ke depan menjadi poin pertimbangan bagi investor sebelum menanamkan modalnya. Dalam ranah statististik, salah satu metode yang dapat digunakan ialah pemulusan eksponensial. Untuk mengatasi tantangan yang timbul saat proses pemodelan, bootstrap aggregating diperkenalkan sebagai pendekatan tambahan. Penelitian ini bertujuan untuk membandingkan performa pemulusan eksponensial pada kondisi dengan dan tanpa bagging serta meramalkan harga emas satu tahun ke depan. Data yang digunakan ialah data harian harga emas dari 4 Januari 2010 s.d 27 Februari 2022. Tipe pemulusan eksponensial yang digunakan ialah Holt’s linear dan the additive damped trend method. Model kemudian dievaluasi berdasarkan MAPE dan RMSE. Hasil pengujian dengan Wilcoxon signed-rank test menunjukkan bahwa penggunaan bagging sebagai pendekaan tambahan terbukti memberikan hasil peramalan yang berbeda nyata. Untuk data harian dan mingguan, model terbaik ialah pemulusan Holt’s linear dengan bagging sedangkan untuk data bulanan, model terbaik ialah pemulusan Holt’s linear tanpa bagging. Pada bulan Februari 2023, diprediksi harga emas akan melampaui Rp1000000/g.
Keyword: bagging, exponential smoothing, gold price, mape, rmse

Judul: COMPARATIVE STUDY OF GOLD PRICE TIME  SERIES DATA USING XGBOOST, STL, AND FACEBOOK PROPHET  METHODS
Abstrak: Harga emas merupakan aspek penting bagi para pelaku pasar karena nilainya yang stabil dan cenderung naik. Penelitian ini membandingkan tiga model analisis data time series harga emas yakni Extreme Gradient Boosting (XGBoost), Seasonal-Trend Decomposition Procedure Based on LOESS (STL), dan Facebook Prophet. Dalam penelitian ini, ketiga model tersebut dievaluasi dengan mempertimbangkan faktor eksternal seperti inflasi dan nilai tukar mata uang. Data harga emas dan faktor eksternal dikumpulkan dari Januari 2010 hingga April 2023. Hasil penelitian menunjukkan bahwa pada pendekatan univariate, model Facebook Prophet memiliki Symmetrical Mean Absolute Percentage Error (SMAPE) sebesar 6,28% dan Mean Absolute Scaled Error (MASE) sebesar 6,0458. Pada pendekatan multivariate, XGBoost memiliki SMAPE sebesar 12,63% dan MASE sebesar 11,815. Dari hasil penelitian, dapat disimpulkan bahwa Facebook Prophet dengan pendekatan univariate lebih akurat dibandingkan pendekatan XGBoost dan STL. Sementara itu, XGBoost dengan pendekatan multivariate lebih akurat daripada Facebook Prophet dalam kasus yang diujikan
Keyword: Emas, Facebook Prophet, Keuangan, peramalan, STL, XGBoost

Judul: Lejeuneaceae Subfamily Ptychanthoideae (Hepaticae) in  West Java
Abstrak: Subfamily Ptychanthoideae of the family Lejeuneaceae (Hepaticae) in West Java is still poorly known. Publications on this subfamily are out of dated and written in the 19th or early of 20th century. The last taxonomic treatment of Ptychanthoideae of West Java was in 1933, many species names have changed since then. Studies on Ptychanthoideae of West Java are urgently needed. Studies on the Ptychanthoideae were based on the specimens collected from West Java. A total number of 361 of specimens deposited in the Herbarium Bogoriense (BO), Herbarium Biotrop (BIOT), Gottingen Herbarium (GOET) and Bangi Herbarium (UKMB) were examined, those are old and several recent specimens collected in West Java. Recent collections were made from Telaga Warna, Ciater, Gunung Halimun Salak National Park, Cibodas Botanical Garden, Bodogol Education Center and Conservation (Gunung Gede Pangrango National Park), University of Indonesia Campus Depok, including several collections from Banten Province. Twenty four species of Lejeuneaceae subfamily Ptychanthoideae are known from West Java, belonging to 8 genera namely Acrolejeunea (Spruce) Schiffn. (2 species), Archilejeunea (Spruce) Schiffn. (1 species), Lopholejeunea (Spruce) Schiffn. (10 species), Mastigolejeunea (Spruce) Schiffn. (3 species), Ptychanthus Nees (1 species), Schiffneriolejeunea Verd. (1 species), Spruceanthus Verd. (2 species) and Thysananthus Lindenb. (4 species). Two new records of Ptychanthoideae: Mastigolejeunea indica Steph. and Thysananthus minor Verdoorn are reported for Java. A determination key to the species is presented including their descriptions and illustrations.
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