Clarification on Lambda2 function object

Functionality to add/problem to solve

The description of the Lambda2 function object states:

The Lambda2 function object computes the second largest eigenvalue of the sum of the square of the symmetrical and anti-symmetrical parts of the velocity gradient tensor.

But it seems the function actually computes the opposite value: -Lambda2

return store ( resultName_, -eigenValues(SSplusWW)().component(vector::Y) );

This is a bit confusing, since negative Lambda2 values are supposed to indicate vortex cores while in OpenFOAM you need to look for positive values to get vortex cores.

Target audience

Anyone using Lambda2 to visualize vortex structures

Proposal

Two possible solutions:

1. writing the actual Lambda2 rather than -Lambda2
2. updating the function description to clearly mention the opposite value of Lambda2 is written

I don't really have a preference between these solutions, as long as the description matches the code to avoid misleading users.

Links / references

This old thread put me on track: https://www.cfd-online.com/Forums/openfoam-post-processing/117005-lambda2-openfoam-utilities.html