Here is the sample code using random data
a=rand(1,50);
b=rand(1,50);
threshold=0.5; % You need to change it to 1e-6 and use original data
i=1;
out= -9999; % setting random data
while out<threshold
out(i)=abs(a(i+1)-a(i))+abs(b(i+1)-b(i));
i=i+1;
end
out
