Judul: Peramalan Nilai Tukar Rupiah Terhadap Dolar Singapura Menggunakan Regresi Linear Sederhana Dan Model ARIMA
Abstrak: Nilai tukar adalah kurs mata uang satu negara yang dinyatakan dalam mata uang negara lain. Tujuan penelitian ini adalah meramalkan nilai tukar rupiah terhadap dolar Singapura dengan menggunakan metode regresi linear sederhana dan model Autoregressive Integrated Moving Average (ARIMA), serta membandingkan keakuratan hasil ramalan kedua metode dengan melihat ukuran kesalahan menggunakan Mean Absolute Percentage Error (MAPE). Metode regresi linear adalah pendekatan yang memodelkan hubungan antara dua variabel, yaitu variabel independen dan variabel dependen. Model ARIMA merupakan sebuah metode peramalan data deret waktu yang menggunakan sifat dan karakteristik dari data historis untuk meramalkan data deret waktu selanjutnya. Kedua metode ini menggunakan data harian nilai tukar rupiah terhadap dolar Singapura selama satu tahun untuk meramalkan satu bulan yang akan datang. Model ARIMA memberikan hasil ramalan yang lebih akurat daripada metode regresi linear sederhana.
Keyword: ARIMA, nilai tukar, peramalan, regresi linear sederhana

Judul: Peramalan Nilai Tukar Rupiah Terhadap Dolar Amerika dengan Pendekatan Analisis Regresi dan ARIMA
Abstrak: Nilai tukar merupakan harga mata uang satu negara yang dinyatakan dalam mata uang negara lain. Nilai tukar berfluktuatif sehingga perlu dilakukan peramalan agar dapat membantu pelaku ekonomi dalam membuat keputusan yang tepat. Fluktuasi nilai tukar dipengaruhi oleh faktor-faktor makroekonomi, seperti inflasi dan jumlah uang beredar. Pengaruh faktor-faktor makroekonomi terhadap nilai tukar dapat dimodelkan dengan regresi linear berganda. Parameter model regresi diestimasi menggunakan metode Ordinary Least Square (OLS). Pada model regresi linear berganda terdapat asumsi-asumsi klasik yang harus dipenuhi. Apabila terjadi korelasi antara residual ke-t dengan residual ke-(t-1), dikatakan residual model mengalami autokorelasi. Dalam karya ilmiah ini, digunakan metode Cochrane-Orcutt untuk mengatasi pelanggaran asumsi tidak adanya autokorelasi pada residual model. Selain faktor makroekonomi, fluktuasi nilai tukar juga dipengaruhi oleh nilai tukar pada periode sebelumnya. Pada karya ilmiah ini dilakukan peramalan nilai tukar rupiah terhadap dolar AS menggunakan metode regresi linear dan ARIMA. Setelah itu, akan dilakukan perbandingan hasil ramalan menggunakan Mean Absolute Percentage Error (MAPE). Hasil peramalan menunjukkan bahwa metode regresi linear memiliki tingkat keakuratan yang lebih baik dibandingkan dengan model ARIMA karena memiliki nilai MAPE yang lebih kecil., Exchange rate is the price of one country’s currency which is expressed in other country’s currency. The exchange rate is volatile so it is necessary to forecast in order to assist economic actors in making the right decisions. Exchange rate fluctuations are influenced by macroeconomic factors such as inflation and money supply. The effect of macroeconomic factors on the exchange rate can be estimated using multiple linear regression. The regression parameters are estimated using the Ordinary Least Square (OLS) method. There are classical assumptions that must be satisfied in multiple linear regression. If there is correlation between the (t)-th residual and the (t-1)-th residual then the residual model has autocorrelation. In this study, the Cochrane-Orcutt method is used to overcome the violation of assumption that there is no autocorrelation in the residual model. The exchange rate fluctuations are also influenced by exchange rate in previous period. In this study, the exchange rate is forecasted using linear regression and ARIMA. Then, their accuracy are compared by evaluating Mean Absolute Percentage Error (MAPE). The forecasting results showed that linear regression has a better accuracy rate than ARIMA model because it has a smaller MAPE value.
Keyword: ARIMA, Cochrane-Orcutt, exchange rate, linear regression

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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