Judul: Analyze Volatility of Large Chilli and Cayenne  Pepper in Indonesia
Abstrak: Komoditas cabai di pasar Indonesia dikenal dalam berbagai jenis di antaranya cabai besar yang terdiri atas cabai merah besar dan cabai keriting serta cabai rawit yang terdiri atas cabai rawit hijau dan cabai rawit merah. Permintaan cabai besar dan cabai rawit memiliki sifat tidak elastis sehingga harganya cenderung volatile. Pola harga yang volatile menyebabkan komoditas cabai termasuk ke dalam kelompok volatile food. Penelitian ini ditujukan untuk mengetahui perbedaan baik pada pola harga cabai besar dan cabai rawit dan volatilitas pada kedua harga cabai tersebut. Metode yang digunakan adalah model ARIMA dan ARCH-GARCH. Hasil penelitian menunjukkan volatilitas yang terjadi pada kedua komoditas tersebut cenderung rendah dan harga cabai rawit memiliki volatilitas yang lebih tinggi dengan koefisien ARCH 0.833003 dibandingkan harga cabai besar yang memiliki koefisien ARCH 0.479061. Harga cabai besar dan cabai rawit memiliki volatilitas yang tinggi yaitu pada periode November sampai dengan Februari. Tingginya volatilitas disebabkan oleh cuaca yang ekstrem sehingga produksi cabai menurun sedangkan permintaan meningkat., The chili commodity in Indonesian market is known in various types, including large chilies consisting of red chilies and curly chilies and cayenne pepper consisting of green cayenne pepper and red cayenne pepper. The demand for large chilies and cayenne pepper is inelastic, so the price tends to be volatile. The volatile price pattern causes the chili commodity to be included in the volatile food category. This study is to determine the differences in both the price patterns of large chili and cayenne pepper and the volatility of the two chili prices. The method that used are ARIMA and ARCH-GARCH models. The results showed that the volatility that occurred in these two commodities tended to be low and the price of cayenne pepper had higher volatility with an ARCH coefficient of 0.833003 compared to the price of large chili which had an ARCH coefficient of 0.479061. The prices of large chilies and cayenne pepper are highly volatile on the November to February. The high volatility was caused by extreme weather so that chili production decreased while demand increased.
Keyword: ARCH-GARCH, ARIMA, Volatility, Cayenne Pepper, Large Chili

Judul: Analysis of Horticultural Commodity Food Price Volatility Before and During the Covid-19 Pandemic
Abstrak: Komoditas hortikultura seperti bawang merah, cabai merah, dan cabai rawit mengalami fluktuasi harga yang sangat berfluktuasi selama tahun 2019–2021. Permintaan komoditas tersebut memiliki sifat tidak elastis sehingga harganya cenderung volatil. Penelitian ini ditujukan untuk menganalisis volatilitas harga bawang merah, cabai merah dan cabai rawit dan menganalisis faktor yang memengaruhi selama periode 2019-2020. Metode yang digunakan adalah analisis coefficient of variation (CV), ARCH-GARCH, dan VECM. Hasil penelitian dengan analisis CV menunjukkan bahwa fluktuasi ketiga komoditas masih berada pada batas wajar. Faktor yang memengaruhi perubahan harga bawang merah di Indonesia pada jangka pendek hanya harga bawang merah domestik, sedangkan pada jangka panjang faktor yang memengaruhi perubahan harga bawang merah Indonesia yaitu nilai tukar, suku bunga, dan inflasi. Untuk cabai merah, faktor yang memengaruhi pada jangka pendek hanya inflasi, sedangkan pada jangka panjang faktor yang memengaruhi perubahan harga cabai merah yaitu inflasi, suku bunga, dan nilai tukar. Hasil IRF menunjukkan bahwa guncangan variabel faktor terhadap perubahan harga bawang merah dan cabai merah Indonesia bervariasi antar periodenya. Hasil FEVD sampai periode lima tahun mendatang menunjukkan semua variabel memiliki persentase kontribusi dalam memengaruhi perubahan harga bawang merah dan cabai merah Indonesia., Horticultural commodities such as shallots, red chilies, and cayenne peppers experienced highly fluctuating prices during 2019 – 2021. Demand for these commodities has an inelastic nature so prices tend to be volatile. This study aims to analyze the price volatility of shallots, red chilies, and cayenne peppers and analyze the influencing factors during the 2019-2020 period. The method used is coefficient of variation (CV) analysis, ARCH-GARCH, and VECM. The results of the research using CV analysis showed that the fluctuations of the three commodities were still within reasonable limits. Factors that affect changes in Indonesian shallot prices in the short term are only domestic shallot prices, while in the long term the factors influencing changes in Indonesian shallot prices are exchange rates, interest rates, and inflation. For red chili, the only influencing factor in the short term is inflation, while in the long term the factors that influence changes in the price of red chili are inflation, interest rates, and exchange rates. The results of the IRF show that the shock of the factor variables to changes in the prices of Indonesian shallots and red chilies varies between periods. The results of the FEVD for the next five years show that all variables have a contribution percentage in influencing changes in the prices of Indonesian shallots and red chilies.
Keyword: ARCH-GARCH, Cayenne Pepper, Onion, Red Chili, Volatility

Judul: Hamiltonian formulation for linear waves motion in two layers fluid
Abstrak: The surface wave could be considered as a wave that separates two fluids, namely water and air. Based on this assumption, it is introduced the interfacial wave, a wave between two layers of fluid with different density. The formulation of interfacial waves motion begins with deriving the base equation of irrotational ideal fluid. Furthermore, according to irrotational fluid assumption, the base equation can be stated in velocity potential. In this derivation, the fluids domain is assumed to be restricted by rigid lid boundary conditions, both at the upper and lower limit. Therefore, the interfacial waves motion can be explained in a hamiltonian formulation. In the hamiltonian formulation, total energy is defined as the sum of kinetic and potential energy. The hamiltonian system is obtained from reduction of kinetic energy by using the Dirichlet Neumann Operator. The resulted kinetic energy equation is nonlinear. Therefore, this form is linearized by first part of the Taylor expansion. This linearization gives a dispersion relation of linear wave. Based on this dispersion relation, the phase speed of the linear wave depends on the density ratio of the two layers fluid.
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