This assignment:
freq = [-pi+pi/L:2*pi/L:pi-pi/L];
is apparently for a two-sided Fourier transform, where ‘L’ is the length of the Fourier transform vector. The increment of the vector is ‘pi/L’, where the ‘/’ is right division (specifically, ‘matrix right division’, see the mrdivide (link) documentation for details). The vector goes from ( -pi + the increment ) to ( pi - the increment ). Supply an integer value for ‘L’ and run that line to see how it works.
