Conservation laws track quantities that must be accounted for, while constitutive relations specify how a material or field responds under particular conditions. In a model, the two are combined in differential equations, allowing variables such as density, velocity, temperature, or displacement to be linked. This pairing connects general mathematical constraints with behavior specific to the modeled medium.
Differential equations alone generally do not specify a unique evolution or spatial configuration. Initial conditions provide the starting state, whereas boundary conditions constrain behavior at the edges of the modeled region. Together, they make the mathematical problem correspond to a particular physical situation and determine which solution can be analyzed or simulated.
A continuous formulation assigns field values across space and time, so calculus and differential equations describe local variation. A discrete model instead represents separate particles or units and tracks their individual states or interactions. The continuous approach is useful when distributed quantities and smooth spatial or temporal change are central to the question.
Modeling begins by selecting field variables that represent the relevant properties, such as density, velocity, temperature, or displacement. Differential equations then express conservation laws and constitutive relations for those variables. The formulation is completed by specifying initial and boundary conditions, after which the equations can be analyzed or simulated to study the system's behavior.
The framework changes its field variables, governing relations, and conditions according to the phenomenon being studied. Velocity and density can describe fluid behavior, displacement can describe elastic deformation, temperature can describe heat transfer, and suitable variables can describe wave propagation. This flexibility lets related mathematical structures address different physical processes without treating them as separate particles.
Analysis examines the differential equations and their conditions to understand how the modeled fields behave, while simulation calculates that behavior for specified situations. Together, these approaches support prediction of changes in density, velocity, temperature, or displacement across space and time. Their results can inform studies in engineering and the natural sciences.