MATLAB: What should I do. HELP function

MATLABmatlab functionnumerical integration

[y, z]=rungeKutta(2,4,0,1,10000)
function dydx=f(x,y,z)
dydx=-2*y + 4*exp(-x) + exp(-1000*(z^2));
end
function dzdx=g(y,z)
dzdx=-y*(z^2)/3;
end
function [y,z]=rungeKutta(y0,z0,x0,xn,n)
h=(xn-x0)/n;
x=x0;
y=y0;
x=x0;
for i=1:n
    k0=h*f(x,y,z);
    l0=h*g(y,z);
    k1=h*f(x+h/2, y+ k0/2, z+ lo/2);
    l1=h*g(y+ k0/2, z+ lo/2);
    k2=h*f(x+h/2, y+ k1/2, z+ l1/2);
    l1=h*g(y+ k1/2, z+ l1/2);
    k3=h*f(x+h, y+ k2, z+ l2);
    l3=h*g(y+ k2, z+ l2);
    y=y + (k0+2*k1+2*k2+k3)/6;
    z=z + (l0+2*l1+2*l2+l3)/6;
end
end

Best Answer

Hi Bilal,
Your code seems to have many undefined variables, like z in line 15, lo in line17, l2 in line 22.
See if the following code works for you and gives the output according to your expectations.
[y, z]=rungeKutta(2,4,0,1,10000)
function dydx=f(x,y,z)
    dydx=-2*y + 4*exp(-x) + exp(-1000*(z^2));
end
function dzdx=g(y,z)
    dzdx=-y*(z^2)/3;
end
function [y,z]=rungeKutta(y0,z0,x0,xn,n)
    h=(xn-x0)/n;
    x=x0;
    y=y0;
    x=x0;
    z=z0; %% z added
    for i=1:n
        k0=h*f(x,y,z);
        l0=h*g(y,z);
        k1=h*f(x+h/2, y+ k0/2, z+ l0/2); %% lo -> l0
        l1=h*g(y+ k0/2, z+ l0/2);
        k2=h*f(x+h/2, y+ k1/2, z+ l1/2);
        l2=h*g(y+ k1/2, z+ l1/2); %% variable name l1 -> l2
        k3=h*f(x+h, y+ k2, z+ l2);
        l3=h*g(y+ k2, z+ l2);
        y=y + (k0+2*k1+2*k2+k3)/6;
        z=z + (l0+2*l1+2*l2+l3)/6;
    end
end
Hope it helps. Thanks.
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