how do i get the difference between two successive values in while loop?

Hi all,

How do I find the difference between a previous value and a current value (‘u_dif’ in code) in a while loop? I get zero values in trying to get this and that affects my expected results.

Thanks

……

for i1 = r:numel(t)
    t2 = ts*i1;

…….

err = 1;       
i2 = 1
while err > 0.03;

          i2 = i2 + 1;
         fz = z0 - Znonlin(i1-1); 

         Fa(i1) = ts*fz.*sin(pp1*(t2)).*exp(n1*(t2));
         FFa(i1) = FFa(i1-1)+Fa(i1);

         Fb(i1) = ts*fz.*cos(pp1*(t2)).*exp(n1*(t2));
         FFb(i1) = FFb(i1-1)+Fb(i1);

    d1 = exp(-n1*t2).*sin(pp1*t2);
         d2 = exp(-n1*t2).*cos(pp1*t2);

         u(i2) = pp2*(FFb(i1).*(Bo.*d1) - FFa(i1).*(Bo.*d2));
    Znonlin(i1)= zlin_a(1,i1) + u(i2);

    u_new(i2) = u(i2);
         u_old(i2)= u(i2-1);

    u_dif(i2) =  u_new(i2)- u_old(i2);%%why zeroes here?
       err = u_dif(i2)/ u_new(i2);

end
Znonlin(i1)

end

Answer 1

[Manikanta Aditya]

Hi Deen,

The updated code:

……

for i1 = r:numel(t)

t2 = ts*i1;

…….

err = 1;

i2 = 0;

while err > 0.03

i2 = i2 + 1;

fz = z0 - Znonlin(i1-1);

Fa(i1) = ts*fz.sin(pp1(t2)).exp(n1(t2));

FFa(i1) = FFa(i1-1)+Fa(i1);

Fb(i1) = ts*fz.cos(pp1(t2)).exp(n1(t2));

FFb(i1) = FFb(i1-1)+Fb(i1);

d1 = exp(-n1*t2).*sin(pp1*t2);

d2 = exp(-n1*t2).*cos(pp1*t2);

u(i2) = pp2*(FFb(i1).(Bo.*d1) - FFa(i1).(Bo.*d2));

Znonlin(i1)= zlin_a(1,i1) + u(i2);

if i2 != 1

u_new = u(i2);

u_old = u(i2-1);

u_dif = u_new- u_old;

err = u_dif/ u_new;

end

Znonlin(i1)

End

As you are incrementing i2 at the beginning of the while loop, you have to initialize the value of i2 to 0. And since there is no error for the first element, we consider that condition and not calculate the error for u(1).