List of Articles ماشین یادگیری جمعی دو سطحی Open Access Article Abstract Page Full-Text 1 - Stock portfolio optimization based on the combined model of omega ratio and mean-variance Markowitz based on two-level ensemble machine learning sanaz faridi Mahdi Madanchi Zaj amir daneshvar shadi shahverdiani fereydoon rahnama 10.30495/jfksa.2022.21083