On Dec 22, 2010, at 1:23 PM, John Peterson wrote:
> Hi Derek,
>
> I don't think there should be any error in computing something like
> \frac{d^2 x}{d \xi^2}, \frac{d^2 x}{d\xi d\eta}, and friends.
Perfect... these are what I am using... and everything seems to be working well
(even for arbitrarily distorted elements).
> The errors are in second derivatives of the shape functions wrt
> physical coordinates, for example (all "d's" should be treated as
> partial derivs)
>
> \frac{ d^2 \phi}{d x^2} = \frac{d \phi}{d \xi} \frac{d^2 \xi}{d x^2} +
> \frac{d^2 \phi}{d \xi^2} (\frac{d \xi}{d x})^2
Indeed - that is what I suspected.
Thanks for the info!
Derek
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