Embedded System Based on an ARM Microcontroller to Analyze Heart Rate Variability in Real Time Using Wavelets

Code 2

C-code to eliminate the linear trend.

void arm_lineal_detrend_f32(float32_t y, int size)

  float32_t a,b,c,d,e,f,x1,x2,C1,C2,determinant;

  int i;

   a=0;b=0;c=0;d=0;e=0;f=0;

   x2=1;

   determinant=0;

   for (i=0; i<size; i++)

       x1=((float32_t)i+1)/(float32_t)size;   // create a slope

       a=a+(x1x1);

       b=b+x1;

       c=c+x1;

       d=d+x2;

       e=e+(x1yi);

       f=f+(x2yi);

  determinant = ad - bc;

  if (isnan(determinant)  isinf(determinant))

      return;

  else

     C1 = (ed - bf)/determinant;    // resolve the System

     C2 = (af - ec)/determinant;    // to find the coefficients C1 and C2

     for (i=0; i<size; i++)

          x1=((float32_t)i+1)/(float32_t)size;

          yi=yi-(x1C1+C2);    // remove lineal trend