Return the final x for different t

I tried to create Runge Kutta 4 order method with 2 matlab files:

1) function [fv]=evalfunc(t,x)

fv=4.0*exp(0.8*t)-x/2.0;

2) close all clear all

a=0;

b=4;

N=25;

h=(b-a)/N;

t=[a:h:b];

x(1)=2;

for i=1:N

    k1 = h*evalfunc(t(i),x(i)); 

    k2 = h*evalfunc(t(i)+h/2,x(i)+k1/2);

    k3 = h*evalfunc(t(i)+h/2,x(i)+k2/2);

    k4 = h*evalfunc(t(i)+h,x(i)+k3);

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

    t(i+1) = a + h*i;

end

A= [t,x];

plot (t,x)

I want to return the result of x(i+1) for every t. Do I just type [t,x]?

How to get t,x result in column of vector ? because when i run the matlab it shown column 1...34 in command window.

Answer 1

[John Petersen]

Matlab defaults to rows. So when creating a vector on the fly like you have, specify both row and column. These lines should be

      x(i+1,1) =x(i) + (k1 + 2*k2 + 2*k3 + k4)/6;

      t(i+1,1) = a + h*i;

to give you columnwise vectors. Alternatively, you could reassign them

x=x(:);
t=t(:);

at the end of the function.