function y = hat(x)
%
%  y = hat(x) returns the value of
%  a hat function:
%   y = 0 for x < 0 and x > 1
%   y = 1 for x >=0 and x <= 1.
%
if x < 0
    y = 0;
elseif x <= 1
    y = 1;
else
    y = 0;
end