/****************************************************************************
Function Name: fAccel
Description: This function calculates the acceleration of a particle at a
certain distance and returns that values to integration routine
returns:double
Input:double,double
************************************************************************/
#include<stdio.h>
#include<math.h>
#include<file.h>
/*define force softening*/
#define EPS 0
double fAccel(double* r,double m,double* radius2,int dim)
	{	
	/*define the variables radius from the center of mass of the particle`
	 *the particle this is for the particle whose acceleration is being
	 determined denoted by dRadius, the radius of the other particle 
	 wrt which the acceleration is being calculated dOtherParticle, 
	 the mass of the other particle dMass. This code will be run 
	 in a loop so all it will additively spit out the 
	 acceleration due to gravity */	
	
		double* dRadius;
		dRadius=r;
		double dDistMag;
		double dMass=m;
		double dGrav;
		double* dOtherParticle;
		dOtherParticle=radius2;
		int iDimensions=dim;
		int i;
	
for(i=0;i<iDimensions;i++)
	{
	dDistMag+=pow(dRadius[i]-dOtherParticle[i],2);
	}


/*calculate the acceleration due to gravity using 
g=dMass*(dRadius-dOtherParticle)/(dRadius-dOtherParticle)^(3/2)
This is run N-1 times where N is the number of particles*/
for(i=0;i<iDimensions;i++)
{	
	dGrav+=-dMass*(dRadius[i]-dOtherParticle[i])/pow(sqrt(dDistMag\
				+pow(EPS,2)),3);		
		}
		return dGrav;
		
	}