Index exceeds the number of array elements. Index must not exceed 1.

I'm trying to apply runge kutta method to my problem but i messed up the code at line34(k1_ivme) and matlab giving this error. What should i do for fix this?

z(1)=-314;
v(1)=0;
h=0.1;
tson=10;
t=0:h:tson;
L=1.5;
vi=0.000001;



n = 100;


for i=1:n-1;
    Re(i)=abs(v(i))*L/vi;
    Cf(i)=0.075/((log(Re)-2).^2);
    k1_hiz(i)=h*v(i);
    k1_ivme=h*(5207.3-3.47*Cf(i)*v(i)^2);

    k2_hiz(i)=h*(v(i)+0.5*k1_ivme(i));
    k2_ivme(i)=h*(5207.3-3.47*(Cf(i)+0.5*k1_ivme)*(v(i)+0.5*k1_ivme))^2;


    k3_hiz(i)=h*(v(i)+0.5*k2_ivme(i));
    k3_ivme(i)=h*(5207.3-3.47*(Cf(i)+0.5*k2_ivme)*(v(i)+0.5*k2_ivme))^2;


    k4_hiz(i)=h*(v(i)+k3_ivme(i));
    k4_ivme(i)=h*(5207.3-3.47*(Cf(i)+k3_ivme)*(v(i)+k3_ivme))^2;
    
    z(i+1)=z(i)+(1/6*(k1_hiz(i)+2*k2_hiz(i)+2*k3_hiz(i)+k4_hiz(i)));
    v(i+1)=v(i)+(1/6*(k1_ivme(i)+2*k2_ivme(i)+2*k3_ivme(i)+k4_ivme(i)));
end

Answer 1

[VBBV]

    z(i+1)=z(i)+(1/6*(k1_hiz(i)+2*k2_hiz(i)+2*k3_hiz(i)+k4_hiz(i)));
    v(i+1)=v(i)+(1/6*(k1_ivme(i)+2*k2_ivme(i)+2*k3_ivme(i)+k4_ivme(i)));

Look at these two lines. you have declared n as 100 and trying to access 101th element . Could that be possible ?

[Esat Akdöngel]

yes its not possible but code gives error at

Index exceeds the number of array elements. Index must not
exceed 1.

Error in sayisal (line 34)
    k1_ivme=h*(5207.3-3.47*Cf(i)*v(i)^2);

here. even if i correct n to n-1 gives same error

[VBBV]

Preallocate array for z. You have set the size of z as 1 element at beginning change it as

n = 100;
z = zeros(n,1)

[VBBV]

You also need to look at last two lines of loop. There are other ways in which initial conditions can be applied into main program.

[Esat Akdöngel]

i think i try to find v(i) values but the problem is they need for the calculation of Re and Cf before matlab calculate them.

Answer 2

[Torsten]

z(1)=-314;
v(1)=0;
h=0.1;
tson=10;
t=0:h:tson;
L=1.5;
vi=0.000001;
n = 100;
for i=1:n
    Re(i)=abs(v(i))*L/vi;
    Cf(i)=0.075/((log(Re(i))-2).^2);
    k1_hiz(i)=h*v(i);
    k1_ivme(i)=h*(5207.3-3.47*Cf(i)*v(i)^2);
    k2_hiz(i)=h*(v(i)+0.5*k1_ivme(i));
    k2_ivme(i)=h*(5207.3-3.47*(Cf(i)+0.5*k1_ivme(i))*(v(i)+0.5*k1_ivme(i)))^2;
    k3_hiz(i)=h*(v(i)+0.5*k2_ivme(i));
    k3_ivme(i)=h*(5207.3-3.47*(Cf(i)+0.5*k2_ivme(i))*(v(i)+0.5*k2_ivme(i)))^2;
    k4_hiz(i)=h*(v(i)+k3_ivme(i));
    k4_ivme(i)=h*(5207.3-3.47*(Cf(i)+k3_ivme(i))*(v(i)+k3_ivme(i)))^2;
    
    z(i+1)=z(i)+(1/6*(k1_hiz(i)+2*k2_hiz(i)+2*k3_hiz(i)+k4_hiz(i)));
    v(i+1)=v(i)+(1/6*(k1_ivme(i)+2*k2_ivme(i)+2*k3_ivme(i)+k4_ivme(i)));
end

Now the code runs, but there must be something wrong with your RK4 integrator.