Index exceeds the number of array elements for runge kutta method

clear all

close all

clc

h =.5; % set the step size

x =[0,4]; % set the interval of x

y = zeros(1,length(x));

yo = 0; % set the intial value for y

n = length(x)-1;

f =@(x,y)-2*x^3+12*x^2-20+8.5; %insert function to be solved

for i = 1:4

k1 = f(x(i),y(i));

k2 = f(x(i)+.5*h,y(i)+.5*k1*h);

k3 = f(x(i)+.5*h,y(i)+.5*k2*h);

k4 = f(x(i)+h,y(i)+k3*h);

y(i+1) = y(i)+((k1+2*k2+2*k3+k4)/6)*h;

end

[t,y_check] = ode45(f,x,2);

plot(x,y)

title('Eulers Method')

figure

plot(x,y_check)

title('ode45 Check')

[John Baumgartner]

I am trying to solve th ODE using the runge Kuuta 4th order method, but keep getting this error in my code. Any suggesttions what I need to fix?

Answer 1

[DGM]

Your loop goes from 1:4

for i = 1:4
    k1 = f(x(i),y(i));

but your vectors only have 2 elements.

x =[0,4];  % set the interval of x
y = zeros(1,length(x));

Did you mean something like this?

x=linspace(0,4,100);