COMSOL Multiphysics™

elempty
If the ind field is not present in an element structure for an element which accepts
a domain grouping, it is defaulted as if all domains belong to group one. Other fields
can usually be specified either per domain group or using one entry valid for all
groups, whether explicitly specified or defaulted as one single group. Note that this
behavior is not explicitly documented for each element type.
Cautionary
Examples
Adding element syntax contributions bypasses all high-level syntax checks, which
can result in unintelligible error messages or even unexpected termination of a
scripting session.
Create a simple model (Poisson’s equation on unit circle) and extract the element
syntax created by meshextend.
clear fem;
fem.geom = circ2;
fem.mesh = meshinit(fem);
fem.shape = 2;
fem.equ.c = 1; fem.equ.f = 1;
fem.bnd.h = 1;
fem.xmesh = meshextend(fem);
elstr = fem.xmesh.getElements;
clear elem;
for i=1:length(elstr)
elem{i} = eval(elstr(i));
end
elstr = fem.xmesh.getInitElements;
clear eleminit;
for i=1:length(elstr)
eleminit{i} = eval(elstr(i));
end
The element syntax can be studied, modified and then fed back into the fem.elem
and fem.eleminit fields. An additional call to meshextend with property
'standard' set to 'off' updates the fem.xmesh field before solving.
fem.elem = elem;
fem.eleminit = eleminit;
fem.xmesh = meshextend(fem,'standard','off');
fem.sol = femstatic(fem);
postsurf(fem,'u');
An elempty element can be used to force a domain group split, which can be
necessary in some cases where subdomain variables are accessed on boundaries. To
the element syntax created above, the following can be added to split the boundary
into two domain groups.
70 | CHAPTER 1: COMMAND REFERENCE