COMSOL Multiphysics™

eleqw
Purpose
eleqw
Define weak form contributions.
Syntax
Description
el.elem = 'eleqw'
el.g{ig} = geomnum
el.geomdim{ig}{edim}.ind{eldomgrp} = domainlist
el.geomdim{ig}{edim}.coeff{eldomgrp}{iequ} = weak
el.geomdim{ig}{edim}.tcoeff{eldomgrp}{iequ} = dweak
el.geomdim{ig}{edim}.ipoints{eldomgrp}{iequ} = ipind
The eleqw element adds weak form contributions to the FEM problem. For the
syntax of the ind field, see elempty. The weak and dweak coefficients have the same
syntax as the corresponding fields in the standard fem struct syntax. See further the
section “Specifying a Model” in the COMSOL Multiphysics Scripting Guide. The
ipoints field differs from the gporder fields in the standard syntax (for example,
fem.equ.gporder) in that it always contains pattern indices instead of orders (see
elgpspec).
The main difference between specifying equations using eleqw and using eleqc is
that the former always gives a correct Jacobian if it is possible to automatically
differentiate all functions called.
Cautionary
Examples
Make sure that the integration point pattern index you use really does exist and
corresponds to a reasonable integration order. When adding an eleqw element to
an existing model, it may be necessary to extract and modify also the default
elgpspec element.
As equation contributions are simply added, it is easy to introduce additional weak
form terms using the fem.elem field.
clear fem;
fem.geom = circ2;
fem.mesh = meshinit(fem);
fem.shape = 2;
fem.equ.c = 1; fem.equ.f = 0;
fem.bnd.h = 1;
fem.elem = {};
clear el;
el.elem = 'eleqw';
el.g = {'1'};
clear equ;
equ.ind = {{'1'}};
equ.coeff = {{'u_test'}};
equ.ipoints = {{'1'}};
el.geomdim{1} = {{},{},equ};
76 | CHAPTER 1: COMMAND REFERENCE