// Program for calculation of a spiral on an apple surface，Jan. 21, 2011.



// file name: apple_spiral.c



#include< stdio.h>

#include< math.h>



void main(void)

{

	double a,pi,c;// a is constant, pi is the Pi and c is adjustment coefficient for number of revolution of spiral.

	double b;// a compression constant towards y direction

	double p, q;// compression coefficients towards x and y directions respectively

	double t,dt;// an intermediate variable and its increment [radian] of Cardioid before the conversion

	double R;// radius of Cardioid before the conversion

	double tmin,tmax;// the minimum and maximum values of the intermediate variable t [radian]

	int i,imax;

	double xx[20001],yy[20001],zz[20001];// Take care of the upper limit of storage memory capacitance.



	FILE *fp;



// setting of the constant

	pi=3.14159265;

	a=1.0; // one of parameters in apple equation

	b=1.2; // one of parameters in apple equation

	p=0.15; // one of parameters in apple equation

	q=0.08; // one of parameters in apple equation

	c=50.0; // adjustment coefficient for number of revolution of spiral  



// setting of the other parameters

	tmin=-pi/2;

	tmax=pi/2;

	dt=(tmax-tmin)/400;// plotting interval of t



// execution of calculation

	i=0;

	for(t=tmin;t<=tmax+dt;t=t+dt)

    {

		i++;



		R=a*(1-sin(t));



		xx[i]=(R*cos(t)*exp(-p*(t-pi/2)*(t-pi/2)))*cos(c*t);

		yy[i]=(R*cos(t)*exp(-p*(t-pi/2)*(t-pi/2)))*sin(c*t);

		zz[i]=b*R*sin(t)*exp(-q*(t-pi/2)*(t-pi/2));



		printf("i=%d,x=%f,y=%f,z=%f\n",i,xx[i],yy[i],zz[i]);

	}

	imax=i;



// writing the calculated coordinates data of the apple spiral into a textfile

	fp=fopen("apple_spiral0.xls","w");

	if(fp==NULL)

	{

		printf("FILE OPEN ERROR\n");

	}

	else

	{

		for(i=1;i<=imax;i++)

		{

			fprintf(fp,"%f,%f,%f\n",xx[i],yy[i],zz[i]);

		}

		fflush(fp);

		fclose(fp);

	}

	printf("end\n");

}// the end of the program