Ensemble Average

the function takes in 3 arguments (cell_name, i, j,en).
The data has to be arranged in a 1x'en' cell, where 'en' is the number of ensembles.
Then each Ensemble is an array of size (i, j).

The output is the ensemble average, and is of same size as the ensembles.

This was tested to find ensemble average in a 2-D turbulent flow signal with 400 time-steps. In order to find the u(fluctuation) and v(fluctuation) from instantaneous u and v.