关于default

The Default setting is also retained when a bordering region is changed. It behaves differently for the different cases, providing the most appropriate option for each combination of regions. For example, if a region is perfectly conducting, its bordering faces can only be perfectly conducting. If this is explicitly set to Perfect electric conductor, the faces will remain perfectly conducting if the region is changed to a dielectric. In most cases this is not appropriate. (A dielectric with a closed perfectly conducting boundary will behave the same way as a perfectly conducting body — unless the sources and field points are all inside the body — but it will result in longer solution times.) However, if the faces on the perfectly conducting region is set to Default they become dielectric boundaries when the region is changed to a dielectric. Note that this means that if a 2D surface (which is perfectly conducting by default) is unioned with a dielectric body, the resulting imprint will again be a dielectric boundary.
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