[Insight-users] itkFEMElement2DC0LinearQuadrilateral and 3DC0LinearHexahedron

[Julia Schnabel]

Hello,

I have a quick question concerning these two classes, in particular 
their method :GetIntegrationPointAndWeight() and ::ShapeFunctions() - 
note that this may apply to other itkFEMElement classes as well but I 
haven't checked:

Could it be that the order of the integration points (and weights) does 
not reflect the node order as indicated by the ::ShapeFunctions() method 
(and the ::ShapeFunctionDerivatives())?

E.g. for the 2D quadrilateral, the integration points are given by:
(0.57735,0.57735),(-0.57735,0.57735),(0.57735,-0.57735),(-0.57735,-0.57735)
whereas the local coordinates for the shape functions are:
(-1,-1),(1,-1),(1,1),(-1,1)

Shouldn't the former be:
(-0.57735,-0.57735),(0.57735,-0.57735),(0.57735,0.57735),(-0.57735,0.57735) 
?

It could be that I'm missing something very obvious here (e.g. the index 
"i" means different things in the two methods).

Thanks for any hints!
Julia

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Julia Schnabel,PhD
Imaging Sciences Institute
Guy's Hospital, King's College London
London SE1 9RT, UK