Error : 'x' undefined

Question

I got a problem with running Octave function (ODE), I\'ve tried already present solutions for this problem but nothing is working. I\'ve also tried by saving my filename as

Answer 1

Since the file starts with function, it is not a script file, as explained in the doc:

Unlike a function file, a script file must not begin with the keyword function

Add any statement (even dummy like 1;) before the function line to get a script file.

# dummy statement to get a script file instead of a function file   
1;

function dx=egzamin(x,t)
  g = 9.81;
  Vx = x(3);
  Vy = x(4);
  dx = [Vx, Vy, 0, -g];
endfunction

N=mod(291813,100);
x1=0;
y1=0;
Vx=20+N;
Vy=20+N;

t=0:0.01:500;
sol=lsode("egzamin",[x1,y1,Vx,Vy],t);
plot(sol(:,1),sol(:,2))

A very clear explanation of what's going on is given here.