Economic Complexity (EC) algorithms estimate the fitness and complexity of the nodes of bipartite networks, such as the network of countries and their exported products. In their application to country-product networks, EC algorithms try to shed light on the hidden capabilities of countries. Capabilities represent the intangible assets driving the development and wealth of countries, such as infrastructures and educational systems. We begin by analyzing the linear Economic Complexity Index (ECI) method, for which a country is fit if it exports complex products. Analogously, a product is complex if fit countries export it. We then study the non-linear Economic Fitness Complexity in its non-homogeneous version (NH-EFC).