/* two-species competition equations */

#include	<stdlib.h>
#include	<stdio.h>
	
#define	DELTAT		0.1
#define	NPERT		((int)(1.0/DELTAT))
#define	MAXTIME 	(200*NPERT)
#define	PRNTTIME	(1*NPERT)

#define	ALPHA1	0.25
#define	ALPHA2	0.25
#define	BETA12	(2.0*0.075) /* b12+b21<1 */
#define	BETA21	(2.0*0.1)
#define	MU1	0.05
#define	MU2	0.05

void Update(double *, double *);

int main(void)
{
	int	ttt;
	double	time, n1, n2;

	n1 = n2 = 0.33;
	time = 0.0;
	for(ttt=0;ttt<MAXTIME;ttt++)
	{
		if(ttt%PRNTTIME==0)
			printf(" %f %f %f\n", time, n1, n2);
		Update(&n1,&n2);
		time += DELTAT;

		if(n1<=0||n2<=0) break;
	}
	return (0);
}

void Update(double *pop1, double *pop2)
{
	double oldpop1, oldpop2;
	oldpop1 = *pop1;
	oldpop2 = *pop2;

	*pop1 += ALPHA1*DELTAT*oldpop1*(1.0-oldpop1-oldpop2) 
		- BETA12*DELTAT*oldpop1*oldpop2 - MU1*DELTAT*oldpop1;
	*pop2 += ALPHA2*DELTAT*oldpop2*(1.0-oldpop1-oldpop2) 
		- BETA21*DELTAT*oldpop1*oldpop2 - MU2*DELTAT*oldpop2;
}