VTKOutput for N1E1Function fails in case of non-FP ValueType

Hi,

I just extended the VTKOutputTest to include all the new function classes for which VTKWriters had been implemented:

• P0Function
• DG1Function
• EGFunction
• N1E1VectorFunction

The test checks that we can compile and execute code for exporting scalar and/or fields over \mathbb{R} represented by these functions, i.e. when the ValueType of the template is real_t. Additionally it also checks whether we can export function objects where ValueType is int32_t and int64_t.

In the case of the N1E1VectorFunction class the integer part fails, because N1E1VectorFunction::communicate() aborts for non-FP types.

if constexpr ( !std::is_floating_point< ValueType >::value )
{
   WALBERLA_ABORT(
       "This function flips the signs of unknowns to accommodate for inconsistent edge orientations. Do not use it to communicate index vectors. Use getDoFs()->communicate instead!" )
}

Admittedly, exporting integer fields is not a feature that is much sought after. However, it can be helpful e.g. in inspecting whether our DoF enumerations work correctly. Actually this is the way the test sets up the fields.

I am not overly familiar with the implementation details of N1E1VectorFunction. However, the abort message suggest that there is a workaround. Would it be possible to have communicate() use that workaround instead of aborting in case of non-FP types?

Cheers
Marcus