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Onbdy()

Its purpose is to define a boundary condition for a Partial Differential Equation (PDE).

The general syntax is

onbdy(ib1, ib2,...) id(u)+<expression>*dnu(u) = g
onbdy(ib1, ib2,...) u = g
where ib's are boundary identification numbers, <expression> is a generic expression and g a generic function.

The term id(u) may be absent as in -dnu(u)=g . dnu(u) represents the conormal of the PDE, i.e.

when the PDE operator is



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