DunnM_hw08_p1_try2.c

/*************************************************************************

Marina Dunn
PHYS 305, Fall 2016
Created: 12 October 2016
Last Modified: 13 October 2016

Purpose: This program is intended to display the orbital motion for an object going around the Sun, based on inputs given by the user. It implements animation programs we have previously used, like demo.c


Usage: The user is prompted to gove a step size, period amount, and initial velocity ratio.

To compile: $gcc DunnM_hw08_p1.c -o DunnM_hw08_p1.exe -lm
To run: $DunnM_hw08_p1.exe

*************************************************************************/

#include <stdio.h>
#include <math.h>
#include "animation.h" //prototypes for the animation routines
#define PI = 3.14159265
#define G = 6.67*pow(10,-11) //m^3/s^2*kg
#define M = 1.989*pow(10,30) // kg, mass of Sun

double acceleration( double r[2], double a[2]);

int main(){

  double t, dt, v_init, L, E, T; // dt is step size
  double r0[2]; //initial position - r0[0] is initial x, r0[1] is initial y
  double v0[2]; //initial velocity - v0[0] is initial x-velocity, v0[1] is initial y-velocity

  double r[2]; //position vector - r[0] is x, r[1] is y
  double v[2]; //velocity vector - v[0] is x-component of v, v[1] is y-component of v
  double a[2]; //acceleration vector - a[0] is x-component of a, a[1] is y-component of a

  double r_mag; //magnitude of position vector
  double v_mag; //magnitude of velocity vector

  double r_half[2];
  double v_half[2];
  double a_half[2];

 int i = 1, count, p1, resample, clock_time;
 count = 0;
 /* time to update animation is 1/20 sec */
 clock_time = 0.05;
 resample=clock_time/dt;

 FILE*fp;
 fp=fopen("orbital.g", "w");

 printf("Please specify an initial velocity as a fraction of sqrt(GM/r): \n");
 scanf("%lf", &v_init);

 printf("Please specify a step size, in AU: \n");
 scanf("%lf", &dt);

 printf("Please specify the total periods that occur: \n");
 scanf("%lf", &T);

 r[0] = 1;
 r[1] = 0;
 v[0] = 0;
 v[1] = (v_init)*2.*PI;

 animation_start( -1.1, 1.1, -1.1, 1.1 );
   set_clock_tick( dt );
   p1 = add_particle(0.0,0.0);

 while(i==1){
 for(t=0; t<T; t+=dt){
   count++;

   r_half[0] = r[0] + v[0]*(dt/2.);
   r_half[1] = r[1] + v[1]*(dt/2.);
   v_half[0] = v[0] + a[0]*(dt/2.);
   v_half[1] = v[1] + a[1]*(dt/2.);

   r[0] += v_half[0]*dt;
   r[1] += v_half[1]*dt;
   v[0] += a_half[0]*dt;
   v[1] += a_half[1]*dt;

 acceleration(r,a);
 r_mag=hypot(r[0],r[1]);
 v_mag=hypot(v[0],v[1]);

 L = (r[0]*v[1]) - (r[1]*v[0]); //conservation of angular momentum for motion in the x,y plane
 E = ((v_mag*v_mag)/2.) + (-G*M/r_mag); //conservation of energy

   if((count==resample)||(t<dt/2.)){
	move_particle_leave_track(p1, cos(t), sin(t) );
	count=0; //reset counter
	}
   }
   }
 printf("E = %lf \n", &E);
 printf("L = %lf \n", &L);
 fclose(fp);
}