thanks for the swift reply. I do expand a valid flowfield in a POD basis. So I collect a time trajectory in phys coordinates, compute the POD modes (similar to a truncated orthonormal basis of the time trajectory phys vectors, if POD basis is unfamiliar) and then expand the flowfield as a linear combination of the POD basis. If the flowfield was part of the sample data in the POD computation, then this is possible with negligible error ( less then 1e-14 relative error ). I can adapt this if necessary, but I am not sure what to do. Do I need to compute the POD basis in local or global coords and then go back to phys? Or maybe something else? Martin On 2021-06-17 18:43, Sherwin, Spencer J wrote:
Hi Martin,
I think it should have been linear provided all vectors are in the polynomial space of your expansion. In your tests is everything in a resolved polynomial space since otherwise you are doing a collocation projections somewhere and this may not be linear.
Cheers, Spencer.
On 17 Jun 2021, at 17:34, Martin Wilfried Hess <mhess@sissa.it> wrote:
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Hello,
I am calling PhysDeriv from an Expansion Class Object.
Why is this not linear?
In the sense that if I call PhysDeriv for any linear combination of vectors it should be the same as computing the linear combination of the PhysDeriv of the vectors.
Martin Hess
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