Will Pazner

The function `GridFunction::GetVectorValue` needs an element index and quadrature point. You are passing a vertex index. You can look at how the function `GridFunction::GetVectorFieldNodalValues` is implemented to see how to...

Hi @tangqi, could you take a look when you get a chance?

You can get the vertices as an integration rule and then follow the example of the snippet that you posted: ```c++ const IntegrationRule *ir = Geometries.GetVertices(pmesh->GetElementGeometry(i)); ```

It looks like you are missing `transf->SetIntPoint(&ir->IntPoint(j));`. (Also, you can call `transf->Weight()` to get the Jacobian determinant directly).

Also: should compression be enabled by default? VTKHDF compression does not require MFEM to be linked with zlib (since the compression is built into the HDF5 library).

@camierjs @helloworld922, any opinions on the default compression? Currently, if MFEM is compiled with zlib, compression will be enabled by default. This makes sense for the standard ParaViewDataCollection (since compression...

It's problem-dependent, but I have seen in the past compression ratios of about 3, and relatively insignificant differences in the runtime, so I think it's worth it to enable by...

@tepperly, thanks for the contribution. Let us know when this is ready for review (either comment here or add the label to this PR).

This PR is now [under review](https://github.com/mfem/mfem/blob/master/CONTRIBUTING.md#pull-requests) (see the table in the PR description). To help with the review process, please **do not force push** to the branch.

@bslazarov, @SchmidtMat, could you take a look at this one? Thanks!