Judul: Periodic Rebalancing of Kompas100 index stock portfolio During COVID-19 Pandemic
Abstrak: Pandemi COVID-19 merupakan peristiwa ekstrem yang mana terjadi dihampir seluruh belahan dunia. Pasar modal Indonesia pun turut terkena dampak COVID-19. Pada Bursa Efek Indonesia, terdapat kelompok saham yaitu Indeks Kompas100. Walaupun Kompas100 memiliki prospek pertumbuhan yang sangat baik, harga saham dari indeks tersebut tetap berfluktuatif yang diakibatkan oleh pergerakan pasar, maka dari itu, investor perlu melakukan rebalancing supaya portofolio Kompas100 mencapai kondisi yang optimum. Tujuan penelitian ini adalah untuk membentuk protofolio saham Kompas100 yang optimal berdasarkan Model Markowitz dan menganalisis strategi periodic rebalancing terhadap kinerja portofolio saham Kompas100 selama pandemi COVID-19. Jenis dan sumber data menggunakan data sekunder berupa data historis harga saham bulanan pada saham Kompas100 mulai Maret 2020 sampai Februari 2021. Berdasarkan hasil analisis dengan model Markowitz, portofolio optimal terdiri atas ASSA 11,25%; KLBF 24,6%; MIKA 24,06%; dan SIDO 40,07%. Disamping itu, monthly rebalancing adalah strategi yang paling optimum dalam meningkatkan return portofolio., The COVID-19 pandemic is an extreme event that has occurred in almost all parts of the world. The Indonesian capital market has also been affected by COVID-19. On the Indonesia Stock Exchange, there was a group of stocks, namely the Kompas100 Index. Although Kompas100 has a very good growth prospect, the stock price of the index is still reflective as a result of market movements, therefore, investors need to carry out rebalancing so that the Kompas100 portfolio can reach its optimum condition. The purpose of this study is to form an optimal Kompas100 stock portfolio based on the Markowitz Model and also to analyze the periodic rebalancing strategy on the performance of the Kompas100 stock portfolio during the COVID-19 pandemic. Types and data sources use secondary data in the form of historical data on monthly stock prices on Kompas100 shares from March 2020 to February 2021. Based on the results of the analysis using the Markowitz model, the optimal portfolio consists of ASSA 11.25%; KLBF 24.6%; MIKA 24.06%; and SIDO 40.07%. In addition, monthly rebalancing is the most optimal strategy for increasing portfolio returns.
Keyword: portfolio, rebalancing, return, risk, stocks

Judul: Optimal Portfolio Formation with Passive and Active Strategies during Pre, Period, and Post Covid-19 Pandemic
Abstrak: Munculnya Pandemi Covid-19 menyebabkan peningkatan inefisiensi dan risiko pasar saham. Untuk mengurangi risiko, dilakukan diversifikasi dengan membentuk portofolio. Dikarenakan investor tidak boleh berinvestasi pada satu sektor saham saja, pembentukan portofolio pada penelitian ini dilakukan pada perwakilan sebelas sektor saham IDX-IC di BEI. Penelitian ini dilaksanakan pada April hingga Juli 2024 menggunakan metode Markowitz dengan strategi pasif dan aktif. Hasil penelitian ini menunjukkan bahwa Pandemi Covid-19 menyebabkan terjadinya penurunan return dan peningkatan risiko portofolio. Ditinjau dari segi komposisi saham, pada periode pra pandemi, sektor yang mencatatkan komposisi terbesar adalah sektor Barang Konsumen Primer, kemudian pada periode masa pandemi yaitu sektor Perindustrian dan Barang Konsumen Non-Primer, dan pada periode pasca pandemi yaitu sektor Keuangan. Strategi optimal pembentukan portofolio jika ingin meminimalkan risiko adalah strategi pasif, sementara jika ingin memaksimalkan return adalah strategi aktif., The emergence of the Covid-19 Pandemic has led to an increase in stock market inefficiency and risk. To decrease the risk, diversification is conducted by forming a portfolio. Due to the investor should not invest in only one stock sector, portfolio formation in this research was conducted on representatives of eleven IDX-IC stock sectors on the IDX. This research was conducted from April to July 2024 using the Markowitz method with passive and active strategies. The results of this research show that the Covid-19 Pandemic causes a decrease in return and an increase in portfolio risk. In terms of stock composition, in the pre-pandemic period, the sector that has the largest composition is the Primary Consumer Goods sector, while in the pandemic period is the Industry and Non-Primary Consumer Goods sectors, and in the post-pandemic period is the Financial sector. The optimal strategy for portfolio formation if you want to minimize risk is a passive strategy, while if you want to maximize returns is an active strategy.
Keyword: Markowitz Method, Optimal Portfolio, Stock, Passive & Active Strategy

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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