Variable names which are defined for use in modeling and postprocessing always represent scalar values. The variable evaluator used inside COMSOL Multiphysics does not recognize vectors, matrices, tensors or operations on such objects. Instead, all such expressions are written in terms of component variables, often with names derived from a common base name using an indexing convention. Under Variable Utilities, both in the Global Defintions branch and in the Definitions branch of each component, you will find a number of utilities for manipulating collections of variables or expressions as if they were the components of a vector, matrix or tensor. The output from these features are represented for use in equations and postprocessing as collections of scalar variables with a common base name, which can also be used in certain nodes under Results to evaluate the complete matrix at once.