In a domain file, you have to declare the Through and Across variables associated with the domain. These variables characterize the energy flow and usually come in pairs, one Through and one Across. Simscape™ language does not require that you have the same number of Through and Across variables in a domain definition, but it is highly recommended. For more information, see Basic Principles of Modeling Physical Networks.
variables begins an Across variables declaration
block, which is terminated by an end key word.
This block contains declarations for all the Across variables associated
with the domain. A domain model class definition can contain multiple
Across variables, combined in a single variables block.
This block is required.
Through variables are semantically distinct in that their values
have to balance at a node: for each Through variable, the sum of all
its values flowing into a branch point equals the sum of all its values
flowing out. Therefore, a domain file must contain a separate declaration
block for its Through variables, with the Balancing attribute
set to true.
variables(Balancing = true) begins a Through
variables definition block, which is terminated by an end key
word. This block contains declarations for all the Through variables
associated with the domain. A domain model class definition can contain
multiple Through variables, combined in a single variables(Balancing
= true) block. This block is required.
Each variable is defined as a value with unit:
domain_var1 = { value , 'unit' };value is the initial value. unit is
a valid unit string, defined in the unit registry. See Declare a Mechanical Rotational Domain for
more information.