There is a discrepancy between how scientists conceive of their models and how they are implemented in a computer program. Informally, scientists represent their models as a composition of many primitive interactions. For example, an ecologist studying an ecosystem with one hundred species examines interactions between pairs of species and takes the full ecosystem to be a composite of these primitive systems. However, when the scientist sits down at a computer to encode the model, this modular structure is lost. The ecologist must simply write down a 100-variable ODE.
This is a companion discussion topic for the original entry at https://blog.algebraicjulia.org/post/2021/01/machines/index.html