A trial function is the starting point for the mode solver. The choice of a trial function determines which mode is found, and the speed of convergence, but it should not affect the accuracy of the computed mode. Just like the refractive index profiles, the trial function can be entered in one of two ways:

- An arbitrary profile can be uploaded as a two-column text file. The first column is the distance and the second column is the refractive index. Click here for an example
- The trial function can be created using a set of built-in functions. Click here for a complete description.