function [v_vect, t_vect] = da(fc,tstop,tstep)
%
% function [v_vect, t_vect] = da(fc,tstop,tstep)
%
% returns the function used by Dong and Atick to fit the time-kernel
% of a LGN X-cell. fc is the temporal cutoff frequency in Hz (usually
% set at 5.5Hz). Time is assumed to be in msec.

fc1 = 2*pi*fc*1e-3; %converts to kHz and circular frequency
t_vect = 0:tstep:tstop; %in msec
v_vect1 = exp(-fc1*t_vect);
v_vect = t_vect.*v_vect1 - (fc1/2) * (t_vect.^2) .* v_vect1;

v_vect = v_vect./max(v_vect);