// math for frequency response of 3-point moving average
//
#include <stdio.h>
#include <math.h>

#define PI (4*atan(1))
#define T (1/8000.0) // sampling period
#define M 101

// H(w) = (1 + D + D*D) / 3
// D = cos(w*T) - j*sin(w*T)
// D*D = cos(2*w*T) - j*sin(2*w*T)
// Magnitude of H(w) is square-root of sum of squares of real and imaginary parts
//
double H(double w) {
  double r = (1 + cos(w*T) + cos(2*w*T))/3, i = (-sin(w*T) - sin(2*w*T))/3;
  return sqrt( r*r + i*i);
}

int main( void)
{
 // Compute and plot magnitude of H(w) using linear scale f = 0 to 4000
 //
  double fmin = 0, fmax = 4000, df = (fmax-fmin)/(M-1), f;

  for( int i = 0; i < M; ++i) {
    f = fmin + i*df;
    printf( "%g %g\n", f, H(2*PI*f) );
  }

  return 0;
}