COMSOL Multiphysics™

elinline
Purpose
elinline
Declare functions and corresponding symbolic derivatives.
Syntax
Description
el.elem = 'elinline'
el.name = fname
el.args{iarg} = argname
el.expr = evalexpr
el.dexpr{iarg} = devalexpr
el.complex = 'true' | 'false'
el.linear = 'true' | 'false'
The elinline element declares a new function with differentiation rules in terms
of other built-in or COMSOL Script or MATLAB functions. COMSOL
Multiphysics calls the function using the MATLAB interpreter if you run COMSOL
Multiphysics with MATLAB and it calls the COMSOL Script interpreter otherwise.
Declared in-line functions can be used with the syntax fname(arg1,arg2,...)
anywhere except for in other in-line function definitions. The args field contains a
list of formal parameter names which can be used in the expr field defining the
function itself and the dexpr field defining derivative expressions with respect to
each of the formal arguments.
The evalexpr and devalexpr expressions can contain any valid expression in the
formal arguments, including COMSOL Script function calls. Global constants and
variables are not available with pi being the only noticeable exception. Note that
differentiation with respect to some formal argument can be disabled by just
specifying the corresponding devalexpr as '0'.
Functions which can generate complex values from real data must have the complex
field set to 'true'. The linear property decides if the function is treated as linear
when deciding whether to reassemble the Jacobian at each time step/iteration or
not.
Cautionary
Examples
Note that in-line functions cannot depend on other in-line functions, only on
built-ins and functions defined on your COMSOL Script or MATLAB path. In-line
functions can be used to override built-ins but can never override another in-line
function.
An in-line function can be used to redefine the derivative of the sqrt function in
such a way that the Jacobian of sqrt(u^2+v^2) will exist for u=v=0.
el.elem = 'elinline';
el.name = 'sqrt';
el.args = {'a'};
el.expr = 'sqrt(a)';
82 | CHAPTER 1: COMMAND REFERENCE