Generates a symmetric para file with fixation periods approximately 25%
of the time.
Kwargs:
n (int, default: 6)
Size of Latin square. Should be equal to the number of
conditions you have.
:note: n must be even. For an odd n, I am not aware of a
general method to produce a Latin square.
Returns:
A numpy.array with each row representing one possible ordering
of stimuli (fixations are coded as 0).