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Multiple scales in space (3)<br />

• “Optimal” method [Herry<br />

et al., 2002]: support is<br />

union of interface nodes.<br />

Exact in 2D plane linear.<br />

• Perfect coupling may be<br />

overconstraining (locking) if<br />

common nodes are scarce.<br />

• Alternative: the “mortar”<br />

method [Bernardi et al., 1990]:<br />

support is one of the two<br />

meshes, usually finest one.<br />

127<br />

Solution of the interface problem<br />

• In all cases we obtain a linear<br />

problem to be solved at the<br />

interfaces, of the form:<br />

H interface operator<br />

HΛ= B<br />

Λ Lagrange multipliers<br />

• H is diagonal in the case of<br />

conforming interface, but not<br />

in the non-conforming case.<br />

• In the presence of cross<br />

points H becomes singular!<br />

Suitable treatment is then<br />

needed for the solution of the<br />

system.<br />

128<br />

64

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