finish effidx vs overlay thickness & rename
update
update comments
add script from Haibo
slight change gridsize
update figure
update Makefile
implement Villar model
working version of eigenvalues
do not use last profile to calculate eigenvalues
Save working eigenvalues.

This is rather wired. If k in `eigs(A, k, sigma)` is small, like 20, the
`eigs` functions warns about only 3/4/5 eigenvalues converge.
remove unused statement
Make grating length shorter to remove the NaN of the peak
update comments
update NOTES
recalc effidx vs overlay thickness
update
update NOTES