n=4;% array length
x=zeros(1,n);% sample array
d=0.4;% value to be added/subtracted
k =跑d(1,n);% uniformly random number between 0 and 1
x(k<0.5)=x(k<0.5)-d;% subtraction
x(k>=0.5)=x(k>=0.5)+d;% addition
many other ways are possible
