using runge kutta 4th order to integrate three different dynamic equation

% silmulating the rossler and lorenz attractor
% rossler is the driver
%lorenze as the response
% dx = [-(x(2)+ x(3));x(1) + a*x(2);b + x(3)*(x(1)-c)]; 
%ds = [sigma*(s(2)- s(1)); s(1) *( rho-s(3))-s(2); s(1)*s(2)-beta*s(3)];
    
% dz = [sigma*(z(2)- z(1));z(1) *( rho-z(3))-z(2);z(1)*z(2)-beta*z(3)];
    a= 0.2; b= 0.2;c= 5.7; sigma= 16; beta= 4; rho = 45.92;g = 0;
    % Define function handles
 dx = [
    -(x(2)+ x(3));
    x(1) + a*x(2);
    b + x(3)*(x(1)-c);
    
    sigma*(s(2)- y(1))-g*(s(1)-x(1));
    s(1) *( rho-s(3))-s(2);
    s(1)*s(2)-beta*s(3);
   
    sigma*(z(2)- z(1))-g*(z(1)-x(1));
    z(1) *( rho-z(3))-z(2);
    z(1)*z(2)-beta*z(3);
    ];
% setting initial conditions
epsu = [0.06;0.01;1];
epsv = [0.85;0.85;1];
epsw = [0.05;0.01;1];
dt = 0.01;
tspan = (dt:dt:1000);
x = zeros(3,tspan(end)/dt);
s = zeros(3,tspan(end)/dt);
z = zeros(3,tspan(end)/dt);
for i = 1: tspan(end)/dt
     time = i*dt;
     k1x = fx(epsu(i), x(i), a,b,c);
     k1y = fx(epsv(i), x(i),s(i),z(i));
     k1z = fx(epsw(i), x(i),s(i),z(i));
     k2x = fx(x(i)+(dt/2),x(i)+(dt/2)*k1x,s(i)+(dt/2)*k1y,z(i)+(dt/2)*k1z);
     k2y = fy(e(x)+(dt/2),x(i)+(dt/2)*k1x,s(i)+(dt/2)*k1y,z(i)+(dt/2)*k1z);
     k2z = fz(e(x)+(dt/2),x(i)+(dt/2)*k1x,s(i)+(dt/2)*k1y,z(i)+(dt/2)*k1z);
     k3x = fx(e(x)+(dt/2),x(i)+(dt/2)*k2x,s(i)+(dt/2)*k2y,z(i)+(dt/2)*k2z);
     k3y = fy(e(x)+(dt/2),x(i)+(dt/2)*k2x,s(i)+(dt/2)*k2y,z(i)+(dt/2)*k2z);
     k3x = fz(e(x)+(dt/2),x(i)+(dt/2)*k2x,s(i)+(dt/2)*k2y,z(i)+(dt/2)*k2z);
     k4x = fx(e(x)+(dt),x(i)+(dt)*k3x,s(i)+(dt)*k3y,z(i)+(dt)*kz);
     k4y = fy(e(x)+(dt),x(i)+(dt)*k3x,s(i)+(dt)*k3y,z(i)+(dt)*kz);
     k4z = fz(e(x)+(dt),x(i)+(dt)*k3x,s(i)+(dt)*k3y,z(i)+(dt)*kz);
     x(i+1)= e(x)+(dt/6) *(k1x +2*k2x +2*k3x +k4x);
     s(i+1)= e(y)+(dt/6) *(k1y +2*k2y +2*k3y +k4y);
     z(i+1)= e(z)+(dt/6) *(k1z +2*k2z +2*k3z +k4z);
end

COMMAND WINDOW: ERROR MESSAGE BELOW

Undefined function or variable 's'.

Error in silmu (line 15)

sigma*(s(2)- y(1))-g*(s(1)-x(1));

Kindly tell me where am wrong please

[Samson]

Hello Jakob. please do you have a code to solve this problem

Answer 1

[Jakob]

In the code you shared, when you call

    sigma * (s (2) - and (1)) - g * (s (1) -x (1));
    s (1) * (rho-s (3)) - s (2);
    s (1) * s (2) -beta * s (3);

s is not defined.