How to compare with the elements before and after

I want know the way to comapre with before element and after element.

Please someone tell me.

I want to comapare V_Ball(index) and V_Ball(index+1).

If V_Ball(index) > V_Ball(index+1) , I wanna break simulation. How should I do?

L1 = 1;
L2 = 1;
M1 = 1;
M2 = 1;
T = 0.01;
Theta1 = -3.14;
Theta2 = 1.57;
V1 = 0;
V2 = 0;
DPendulum = classDoublePendulum(L1,L2,M1,M2,Theta1,Theta2,V1,V2,T);
for i = 1:200
    Trq1 = -10;
    Trq2 = -10;
    DPendulum.pstep(Trq1,Trq2);
    V = DPendulum.AngleVelocity2;
    Angle = cos(DPendulum.Theta2);
    V_Ball(i) = V*Angle;
    for index = 1 : length(V_Ball)
     if abs(V_Ball(index)) - abs(V_Ball(index+1:end)) > 0% compare elements before after
         disp(true);
     else
         disp(false);
     end
    end
   
    
   
   
 end

Answer 1

[Davide Masiello]

Your condtional statement says

if abs(V_Ball(index)) - abs(V_Ball(index+1:end)) > 0

which is wrong, beacuse when index=length.V_Ball than index+1 is larger than the size of V_Ball.

Plus, your are checking your statement over the whole array V_Ball at each iteration of the outer loop, while I think you just need to do that for the last two elements.

Another issue is that you are using the absolute value in the conditional statement, which makes it a bit ambiguous because you are not actually checking that V_Ball(index) > V_Ball(index+1) .

Now, I am not sure I correctly understand your problem, but I think this might be a solution

for i = 1:200
    Trq1 = -10;
    Trq2 = -10;
    DPendulum.pstep(Trq1,Trq2);
    V = DPendulum.AngleVelocity2;
    Angle = cos(DPendulum.Theta2);
    V_Ball(i) = V*Angle;
    if i = 1
    elseif V_Ball(i-1) > V_Ball(i)
        disp(true);
        break
    else
        disp(false);
    end
end