#include <stdio.h>
#include<stdlib.h>
#include <g2.h>
#ifdef WIN32
#include<g2_win32.h>
#define WINTYPE 0
/* gcc g2_shm.c -DWIN32 -lg2 -lm -lkernel32 -lgdi32 -luser32 -lcomdlg32 -o g2_shm.exe */
#endif
#ifdef XWIN
#include<g2_X11.h>
#include <unistd.h> /* so I can use pause() */
#define WINTYPE 1
/* gcc g2_shm.c -o g2_shm -DXWIN -L/usr/X11R6/lib64 -L/usr/local/lib -lg2 -lm -lX11 -lXext -lgd */
#endif

int main()
{
    int i, dev, dev1,white, black,red;
    float x,v,x0,v0,h,t,l1,l2,k1,k2,k3,l3,E0,E;
    char strx[256],strv[256];
    h = 0.02;
    x = 1.0;
    v = 0.0;
    if(WINTYPE==1)
	dev1=g2_open_X11(300,300);
    if(WINTYPE==0)
	dev1=g2_open_win32(300,300,"RH",0);
    g2_set_auto_flush(dev1,0);
    white=g2_ink(dev1, 1.0, 1.0, 1.0);
    black=g2_ink(dev1, 0.0, 0.0, 0.0);
    sprintf(strv, "%s", "v");
    sprintf(strx, "%s", "x");
    
    for(i=1;i<6000;i++){
	k1=h*v;
        l1=-2.0*h*x*x*x;
        k2=h*(v+0.5*l1);
       	l2=-2.0*h*(x+0.5*k1)*(x+0.5*k1)*(x+0.5*k1);
        k3=h*(v+l2);
       	l3=-2.0*h*(x+k2)*(x+k2)*(x+k2);
        v=v+(l1+4.0*l2+l3)/6.0;
        x=x+(k1+4.0*k2+k3)/6.0;  
	g2_pen(dev1, black);
	g2_line(dev1, 150.0, 0.0, 150.0, 300.0);
	g2_string(dev1, 155.0, 290.0, strv);    
	g2_line(dev1, 0.0, 150.0, 300.0, 150.0);
	g2_string(dev1,290.0, 140.0, strx);
        g2_circle(dev1, 150.0+100.0*x, 150.0+100.0*v, 3);
	g2_flush(dev1);
	if(WINTYPE==1) usleep(1);
	g2_pen(dev1, white);
	g2_filled_rectangle(dev1, 0,0,300,300);
    }
    g2_flush(dev1);
    g2_close(dev1);
    return(0);
}