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: Analysis of Optimal Stock Portfolio Formation during the Covid-19 pandemic with Multi-Index Models
Abstrak: Covid-19 berdampak ke sistem perekonomian, salah satunya dalam investasi saham. Risiko dalam investasi dapat diperkecil dengan membentuk portofolio. Karya ilmiah ini bertujuan mencari portofolio optimal dengan menggunakan model Multi Indeks. Model Multi Indeks menggunakan lebih dari satu indeks untuk menghitung expected return, sehingga dimungkinkan lebih akurat. Saham yang digunakan adalah saham yang tergabung di indeks LQ45 periode 1 Maret 2020 sampai 1 April 2021. Indeks pasar yang digunakan adalah IHSG, sedangkan indeks non-pasar adalah Dow Jones Industrial Average dan Hang Seng. Berdasarkan hasil penghitungan, portofolio optimal dibentuk dari 96.196498% saham TOWR dan 3.803502% ACES memiliki expected return harian sebesar 0.09047297% dengan risiko sebesar 2.52761%., Covid-19 has effect on the economic system, one of which is stock investment. The risk in investing can be minimized by forming a portfolio. The aim of this study is to determine the optimal portfolio using the Multi Index model. The Multi Index Model uses more than one index to calculate the expected return, so it is possible to be more accurate. The stocks used are stocks that are members of the LQ45 index for the period March 1, 2020 to April 11, 2021. The market index used is the IHSG, while the non-market indexes are the Dow Jones Industrial Avarage and the Hang Seng. Based on the calculation results, the optimal portfolio is formed from 96.196498% of TOWR stocks and 3.803502% of ACES which has an estimated daily return of 0.09047297% with a risk of 2.52761%.
Keyword: Covid-19, multi index model, portfolio

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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