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# Need Help on Matlab code PLEASE

Posts: 1Member
This code is using the 4th Order Runge-Kutta Method to solve for the orbit of Halley's comet over time. I don't know why it won't work. I'm given the initial x0 vector and h is the step size. Any help would be appreciated.

function [A] = matrix(x1, x3, x5)

r = sqrt((x1)^2 + (x3)^2 + (x5)^2)

m = 4*pi^2

b = -m/r^3

A = [0 1 0 0 0 0;
b 0 0 0 0 0;
0 0 0 1 0 0;
0 0 b 0 0 0;
0 0 0 0 0 1;
0 0 0 0 b 0];

function [Y] = rk4(x0, h)

T = 30;

n = T/h - 1;

x(1) = x0(:,1);

for i = 2:n

A = matrix(x(i-1,1), x(i-1,3), x(i-1,5));

k1 = A.*x(:,i-1);
k2 = A.*(x(:,i-1) + .5*h*k1);
k3 = A.*(x(:,i-1) + .5*h*k2);
k4 = A.*(x(:,i-1) + h*k3);

phi = (1/6)*(k1 + 2*k2 + 2*k3 + k4);

x(:,i) = x(:,i-1) + phi*h;

end

Y = x