/////////////////////////////////////////////////////////////////////////////////
// Solve IVP 
// x''+w^2x=0 , x(0)=0, x'(0)=v0  (1)
// over the interval 0<t<T with forward Euler method.
// Analytical solution: x(t)=(v0/w)sin(wt)
// The time steps are h={0.05, 0.025}.
// We rewrite (1) as a system of 2 first order ODE's
// x'=y, y'=-w^2x, x(0)=0, y(0)=v0
///////////////////////////////////////////////////////////////////////////////////
/*compile with	
gcc -o aufgabe3 aufgabe3.c  -L/usr/local/dislin -ldislnc -lm -lX11
or
gcc -std=c99 -o aufgabe3  aufgabe3.c -I(DISLIN_PATH) -L(DISLIN_PATH) -ldislin
*/

#include <stdio.h>
#include <math.h>
#include "/usr/local/dislin/dislin.h"  /*path to the dislin library*/

int main()
{
         metafl("XWIN");  // output into (small) screen
         //metafl("CONS"); // output into full screen
        scrmod("REVERS"); // reverse colors; works for screen output, PS, TIFF and PNG files
//--------------------------------------------------
   /*     metafl("PNG"); // output format
	setfil("test.png"); // name of the output file
	scrmod("REVERS"); // reverse colors
        winsiz(1280,640); // relosution of image file
	page(2970*2,2970);// define a plot size*/
//----------------------------------------------------
disini();  //dislin initialisation
         int w=1;
         int v0=1;       
	float x = 0.0; // initial space 
        float y = v0; // initial space 
	float t = 0.0; //initial time
	float h = 0.025; // time step
        float Tend = 50; //end of the time interval

        name("x","x"); //axis labels 
        name("y","y");
	graf(-6,6,-6,1,-3,3,-3,1); // plots a two-dimensional axis system
      

  //     setrgb(0,0,1); // set blue color
/*	while ( t <= Tend ) {
		x = x + h*y;
                y =  y-h*w*x;
		t = t + h;
		rlsymb(21,x,y); // plot the symbol (t,x)one the plane
	}     
  */

disfin(); //finish dislin 

printf("READY\n"); //print READY at the end of the program
}