Hi Samuel, The issue with the symmetric tensor magnitude calculation is that ParaView doesn't know it's a symmetric tensor so it doesn't know that it needs to sum the off-diagonal values twice. All that is know for these arrays are how many components there are. A three-component array could be representing either a 3D vector or a 3D anti-symmetrix, second order tensor so it's the user's responsibility to compute the magnitude properly where "shortened" representations of tensors are used.
Regards, Andy On Sat, May 23, 2015 at 12:03 PM, Samuel Key <samuel...@bresnan.net> wrote: > Reference: ParaView Version 4.3.1 > > I have two technical questions: > > (Q1) In the PV filter 'Gradient Of Unstructured Data Set' is the > "QCriterion" function, the Q-Criterion defined by J. C. R. Hunt, A. Wray, > and P. Moin (1988) "Eddies, stream, and convergence zones in turbulent > flows," Center for Turbulence Research Report CTR-S88, and referenced by G. > Haller in "*An objective definition of a vortex*," J. Fluid Mech. (2005), > vol. 525, pp.1–26? > > (Answer to Q1) Courtesy of Don Simons of Egility Corp., Yes, the formula > being > Q=-0.5*(Vx,x*Vx,x + Vy,y*Vy,y + Vz,z*Vz,z) - (Vx,y*Vy,x + Vx,z*Vz,x + > Vy,z*Vz,y) > > (Q2) In the PV filter 'Calculator' what is the formula used by the "mag" > function to calculate mag(*S*) where *S* is a symmetric 2nd-order tensor? > Using matrix notation, the tensor *S* would have the following components: > > --------------- > | Sxx Sxy Sxz | > | Sxy Syy Syz | > | Sxz Syz Szz | > --------------- > > (Answer to Q2) The PV formula for mag(*S*) is the square root of the sum > of the squares of the 6-tuple (Sxx, Syy, Szz, Sxy, Sxz, Syz). > > For consistency with a three-component vector, I would have expected it to > be the 6-tuple (Sxx, Syy, Szz, 2Sxy, 2Sxz, 2Syz)? > > > Samuel W Key > FMA Development, LLC > 1005 39th Ave NE > Great Falls, Montana 59404 > USA > > _______________________________________________ > Powered by www.kitware.com > > Visit other Kitware open-source projects at > http://www.kitware.com/opensource/opensource.html > > Please keep messages on-topic and check the ParaView Wiki at: > http://paraview.org/Wiki/ParaView > > Search the list archives at: http://markmail.org/search/?q=ParaView > > Follow this link to subscribe/unsubscribe: > http://public.kitware.com/mailman/listinfo/paraview > >
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