Judul: Penerapan Algoritma C4.5 dan Random Forest pada Tingkat Penjualan Serum Somethinc di Shopee
Abstrak: Kegiatan jual beli online di Indonesia semakin meningkat. Shopee merupakan platform jual beli online dengan kunjungan tertinggi di Indonesia pada kuartal IV tahun 2022. Kategori barang yang memiliki transaksi tertinggi di Shopee adalah produk kecantikan. Brand Somethinc merupakan produk kecantikan lokal yang sangat sukses di Shopee dengan menempati peringkat pertama dalam penjualan produk serum di Indonesia. Penelitian ini menerapkan metode klasifikasi C4.5 dan Random Forest untuk melihat peubah penting dalam penjualan serum Somethinc di Shopee. Peubah yang digunakan berasal dari profil toko yang meliputi: jumlah pengikut, jumlah produk, performa pesan, rating toko, dan waktu bergabung. Data penjualan yang kontinyu didiskritisasi menggunakan k-means menjadi data ordinal dengan tingkat rendah, sedang, tinggi, dan sangat tinggi. Terdapat ketidakseimbangan pada kelas penjualan sehingga dilakukan teknik SMOTE. Penerapan teknik SMOTE meningkatkan nilai akurasi dan F1-score. Algoritma C4.5 menghasilkan pohon keputusan yang berisikan aturan dalam klasifikasi. Random Forest menghasilkan urutan kepentingan peubah berdasarkan nilai MDG berturut-turut dari tinggi ke rendah yaitu: jumlah pengikut, jumlah produk, performa pesan, waktu bergabung, dan rating toko., Online buying and selling activities in Indonesia are increasing. Shopee is an online buying and selling platform with the highest visits in Indonesia in the fourth quarter of 2022. The category with the highest transactions at Shopee is beauty products. Somethinc is a very successful local beauty product at Shopee which have highest sales of serum products in Indonesia. This study applies the classification method C4.5 and Random Forest to see important variables in the sales of Somethinc serum at Shopee. The variables used come from store profiles which include: number of followers, number of products, chat performance, store rating, and length of stay. Continuous sales data is discretized using k-means into ordinal data with low, medium, and high levels. There is an imbalance of data in the sales class so that the SMOTE technique is used. The C4.5 algorithm produces a decision tree that contains rules for classification. Random Forest generates the order of variable importance based on the Mean Decrease Gini (MDG) values in descending order, which are as follows: number of followers, number of products, message performance, joining time, and store rating.
Keyword: Algoritma C4.5, Random Forest, k-means, serum Somethinc, Shopee

Judul: Pengaruh Online Consumer Review dan Rating  terhadap Purchase Intention Produk Serum Somethinc pada Marketplace Shopee di Jabodetabek
Abstrak: Peningkatan jumlah pengguna internet menciptakan banyak peluang bagi para pengusaha, sehingga mengakibatkan peningkatan jumlah e-commerce dan marketplace di Indonesia. Shopee adalah salah satu marketplace Indonesia yang menawarkan fitur online consumer review dan rating di platform. Tujuan penelitian ini menganalisis pengaruh online consumer review dan rating terhadap purchase intention produk serum Somethinc pada marketplace Shopee. Jenis penelitian ini adalah penelitian kuantitatif dengan teknik pengambilan sampel purposive sampling. Data penelitian dikumpulkan pada bulan April – Mei 2023 melalui kuesioner dari 150 responden di Jabodetabek sebagai data primer dan melalui studi literatur dari buku, jurnal, dan artikel terkait sebagai data sekunder. Penelitian ini menggunakan metode analisis deskriptif dan Structural Equation Modeling-Partial Least Square (SEM-PLS). Hasil penelitian menunjukkan variabel online consumer review dan rating berpengaruh signifikan dan positif terhadap purchase intention produk serum Somethinc dengan variabel rating memiliki pengaruh lebih dominan., The increase in the number of internet users creates many opportunities for entrepreneurs, resulting in an increase in the number of e-commerce sites and marketplaces in Indonesia. Shopee is one of the Indonesian marketplaces that offers online consumer review and rating features on its platform. The purpose of this study was to analyze the effect of online consumer review and rating on purchase intention of Somethinc serum products on Shopee marketplace. This type of research is quantitative research with purposive sampling technique. The research data was collected in April - May 2023 through questionnaires from 150 respondents in Jabodetabek as primary data and through literature studies from books, journals, and related articles as secondary data. This research uses the descriptive analysis method and Structural Equation Modeling-Partial Least Square (SEM-PLS). The results showed that the online consumer review and rating variables had a significant and positive effect on the purchase intention of Somethinc serum products with the rating variable having a more dominant influence.
Keyword: online consumer review, purchase intention, rating, Shopee, Somethinc  serum

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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