COMSOL Multiphysics™

femdiff
Use the field fem.rules to specify additional differentiation rules. The derivative of
the inverse hyperbolic tangent function atanh can, for example, be specified as
{'atanh(x)','1/(1-x^2)'}.
It can also be stored as a field in the FEM structure.
Assume a user-defined function foo(a,b) has been written, implementing the
analytical expression a^2+a*sin(b^3). The derivatives of this function are specified
as:
'rules', {'foo(a,b)', '2*a+sin(b^3),3*a*b^2*cos(b^3)'}
femdiff does not support functions with string arguments.
Cautionary
The relational and Boolean operators have been included for convenience only, and
must be used with extreme caution. Their symbolic derivative is considered to be
identically 0.
Coefficient M-files are not allowed in the input.
Compatibility
The function flgetrules for converting FEMLAB 1.0/1.1 differentiation rules is
no longer available.
The properties bdl, out, rules, and sdl are obsolete in FEMLAB 3.0.
The fields fem.equ.varu and fem.bnd.varu, etc. are no longer generated in
FEMLAB 3.0.
The precedence rules for the operators | and & have been changed to comply with
MATLAB 6.0 precedence.
The differentiation algorithm is new in FEMLAB 1.2. The @fldiffobj class is
obsolete.
See Also
femnlin
120 | CHAPTER 1: COMMAND REFERENCE