Problem: Eigen3 find script is not updated in master branch / calculation of sigma weights on windows corrupted

[rigra]

Details:

1. in develop branch the Eigen3 find script was already updated but not in the master branch
2. on windows x64 machine, the calculation of the sigmaweights_m does not lead to the sum of 1 which is necessary (W_m_0 + L* W_m_i == 1)
   Solution:
3. cherry pick the commit of the updated Eigen3 find script
4. change the calculation of W_m_i to a mathematical equivalent formula with better results on windows x 64

[mherb]

First of all, thank you very much for your contribution!

I have a couple of requests here before merging:

1. Could you make two separate PRs for the eigen cherry-pick and the numerics issue?
2. I'd prefer to have clean PRs without tons of re-formatting and a dozen commits that actually change a single line, so while re-creating the PRs, could you maybe cleanup the actual changes into a single commit changing only what has actually changed?
3. (optional) Can you make a unit-test for the numerics issue to avoid future regressions with regard to this?

Thanks!

[rigra]

Hi,
I will close this PR and set up two new one.

[rigra]

#26 and #27 substitute this