what should I do. HELP function

[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

[Bilal Ates]

You are a great detail....

Answer 1

[Gaurav Aggarwal]

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.

[Bilal Ates]

You are a great detail....

[Gaurav Aggarwal]

Did it work for you? If so, it would be great if you accept the answer and close this query. Thanks.

[Bilal Ates]

worked. I thank you

Answer 2

[Steven Lord]

As stated on this documentation page "Script files cannot have the same name as a function in the file." Either rename your script file to something other than rungeKutta.m or rename the function you define on line 9 of rungeKutta.m to something other than rungeKutta.

[Gaurav Aggarwal]

After defining some variables, the script worked for me. The script's name and the function name were same in my case. As per my understanding, it doesn't matter as long as the function call is within the file scope, which seems to be the case with Bilal's (acc. to the code he provided).

[Bilal Ates]

Thank you all for your help