midpnt.c
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	#define FUNC(x) ((*func)(x))

	double midpnt(double (*func)(double), double a, double b, int n)
	{
	double x,tnm,sum,del,ddel;
	static double s;
	int it,j;

	if (n == 1) {
	return (s=(b-a)FUNC(0.5(a+b)));
	} else {
	for(it=1,j=1;j<n-1;j++) it *= 3;
	tnm=it;
	del=(b-a)/(3.0*tnm);
	ddel=del+del;
	x=a+0.5*del;
	sum=0.0;
	for (j=1;j<=it;j++) {
	sum += FUNC(x);
	x += ddel;
	sum += FUNC(x);
	x += del;
	}
	s=(s+(b-a)*sum/tnm)/3.0;
	return s;
	}
	}
	#undef FUNC