看留言有人想选择圆的边界，实现方法倒是有好多种，分别针对不同的情况。

例1，如图选择几何模型中圆部分的边界。这里圆所在的domain还是要自己选择下，暂时没有好办法，但是如果用CwM做的几何，这倒是还是蛮好控制的，详见例3。

实现方法：

实质上是调用了Explicit选择的，Output Entities,Adjacent

boundaries，用户可以GUI做，这里不再熬述。

% This is a script for Comsol(4.x) with

Matlab.

% Get boundaries of specific domains.

%

% Copyright to mxio at Shanghai

University.

%

%

mxio

%

18,July,2013

import com.comsol.model.*

import com.comsol.model.util.*

%--------------------------------------------------------------------

% Create a geometry

model = ModelUtil.create('Model');

model.modelNode.create('mod1');

model.geom.create('geom1', 2);

model.geom('geom1').feature.create('c1', 'Circle');

model.geom('geom1').feature('c1').set('r', '0.1');

model.geom('geom1').feature.create('arr1', 'Array');

model.geom('geom1').feature('arr1').selection('input').set({'c1'});

model.geom('geom1').feature('arr1').setIndex('fullsize', '5', 0);

model.geom('geom1').feature('arr1').setIndex('fullsize', '4', 1);

model.geom('geom1').feature('arr1').setIndex('displ', '0.3', 0);

model.geom('geom1').feature('arr1').setIndex('displ', '0.', 1);

model.geom('geom1').feature('arr1').setIndex('displ', '0.3', 1);

model.geom('geom1').feature.create('r1', 'Rectangle');

model.geom('geom1').feature('r1').setIndex('size', '1.6', 0);

model.geom('geom1').feature('r1').setIndex('size', '1.3', 1);

model.geom('geom1').feature('r1').setIndex('pos', '-0.2', 0);

model.geom('geom1').feature('r1').setIndex('pos', '-0.2', 1);

model.geom('geom1').run;

%--------------------------------------------------------------------

% Create a selection

model.selection.create('sel1', 'Explicit');

model.selection('sel1').geom('geom1', 2, 1, {'exterior'});

model.selection('sel1').set([2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21]);

%--------------------------------------------------------------------

% Verify the selection contains the boundaries of

specific domains

model.physics.create('c', 'CoefficientFormPDE', 'geom1', {'u'});

model.physics('c').feature.create('dir1', 'DirichletBoundary', 1);

model.physics('c').feature('dir1').selection.named('sel1');

%--------------------------------------------------------------------

mphviewselection(model, 'sel1');

mphsave(model,'circle_boundary');

例2，如图选择几何模型外边界。

% This is a script for Comsol(4.x) with

Matlab.

% Get exterior boundaries.

%

% Copyright to mxio at Shanghai

University.

%

%

mxio

%

18,July,2013

import com.comsol.model.*

import com.comsol.model.util.*

model = ModelUtil.create('Model');

model.modelNode.create('mod1');

%--------------------------------------------------------------------

% Create a geometry

model.geom.create('geom1', 2);

model.geom('geom1').feature.create('sq1', 'Square');

model.geom('geom1').feature.create('sq2', 'Square');

model.geom('geom1').feature('sq2').set('size', '0.5');

model.geom('geom1').feature('sq2').setIndex('pos', '0.', 0);

model.geom('geom1').feature('sq2').setIndex('pos', '0.8', 0);

model.geom('geom1').feature('sq2').setIndex('pos', '0.2', 1);

model.geom('geom1').feature.create('c1', 'Circle');

model.geom('geom1').feature('c1').set('r', '0.3');

model.geom('geom1').feature('c1').setIndex('pos', '0.5', 0);

model.geom('geom1').feature('c1').setIndex('pos', '0.9', 1);

model.geom('geom1').runAll;

%--------------------------------------------------------------------

% Create a selection

model.selection.create('sel1', 'Explicit');

model.selection('sel1').all;

model.selection.create('adj1', 'Adjacent');

model.selection('adj1').set('input', {'sel1'});

model.selection('adj1').set('exterior', 'on');

model.selection('adj1').set('interior', 'off');

%--------------------------------------------------------------------

mphviewselection(model, 'adj1');

mphsave(model,'exterior_boundary');

例3， 在一个方形中，画一系列的圆，并选择这些圆的边界。

% This is a script for Comsol(4.x) with

Matlab.

% Get circle boundaries.

%

% Copyright to mxio at Shanghai

University.

%

%

mxio

%

18,July,2013

import com.comsol.model.*

import com.comsol.model.util.*

model = ModelUtil.create('Model');

model.modelNode.create('mod1');

model.geom.create('geom1', 2);

%--------------------------------------------------------------------

% Model Parameters

sq_length = 1;

cl_num = 10;

cl_radius = 0.03*sq_length;

cl_x = linspace(0.1*sq_length,0.9*sq_length,10);

cl_y = (0.2*sin(4*pi*cl_x)+0.5)*sq_length;

%--------------------------------------------------------------------

model.geom('geom1').feature.create('sq1', 'Square');

model.geom('geom1').feature('sq1').set('size', num2str(sq_length));

cl_selection_name = cell(1,cl_num);

for i = 1:cl_num

cl_name = ['c', num2str(i)];

cl_selection_name{i} = ['geom1_',cl_name,'_dom'];

model.geom('geom1').feature.create(cl_name, 'Circle');

model.geom('geom1').feature(cl_name).set('createselection', 'on');

model.geom('geom1').feature(cl_name).set('r', num2str(cl_radius));

model.geom('geom1').feature(cl_name).setIndex('pos', num2str(cl_x(i)), 0);

model.geom('geom1').feature(cl_name).setIndex('pos', num2str(cl_y(i)), 1);

end

model.geom('geom1').runAll;

%--------------------------------------------------------------------

% Create a selection

model.selection.create('uni1', 'Union');

model.selection('uni1').set('input', cl_selection_name);

model.selection.create('adj1', 'Adjacent');

model.selection('adj1').set('input', {'uni1'});

mphviewselection(model, 'adj1');

mphsave(model,'cricle_boundary');

mxio

2013.7.18