## Estimated Effective Index

The convergence of the program is primarily influenced by the estimated
effective index and the trial function.
For example, to find the
fundamental mode of a waveguide, choose the highest index in the structure
as the estimated effective index, and a symmetric function as a trial function.

If the estimated effective index is lower than any guided mode of the structure,
the result will converge towards a radiation mode.

Sometimes it might be useful to repeatedly run the program
with different estimated effective indices to search for the existence of separate modes.
To use this feature, the effective index should be entered as a range value
such as:

**1.45 10 1.50**

This will run the program using ten different estimated effective indices between
1.45 and 1.50. Plots are not generated for each iteration.
Therefore,
the console output from the program must be examined to determine the modes.