Systems of Differential Equations

Abstract

Chapters 1 and 2 presented a view of the environment as a series of fields distributed across space and evolving in time. While fields provide the ultimate description of the state of the environment, there are times when models can be simplified significantly by ignoring the spatial inhomogeneity of fields throughout a region of space. This simplification is completely valid when the field is homogeneous throughout that region, but it also may be at least partially valid if the effect ultimately of interest (e.g. human health) depends on some average property of the field, such as the mean, rather than on the variability in space.