pprz_stat.c

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/*
 * Copyright (C) 2017 Kirk Scheper
 *
 * This file is part of paparazzi.
 *
 * paparazzi is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * paparazzi is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with paparazzi; see the file COPYING.  If not, see
 * <http://www.gnu.org/licenses/>.
 */
 
#include "math/pprz_stat.h"
 
/*********
 * Integer implementations
 *********/
 
int32_t mean_i(int32_t *array, uint32_t n_elements)
{
 
  if (n_elements == 0) {
    // Note that something else is wrong if you want the mean of 0 samples.
    return 0;
  }
  // determine the mean for the vector:
  float sum = 0.f;
  uint32_t i;
  for (i = 0; i < n_elements; i++) {
    sum += (float)array[i];
  }
  return (int32_t)(sum / n_elements);
}
 
int32_t variance_i(int32_t *array, uint32_t n_elements)
{
  return (covariance_i(array, array, n_elements));
}
 
int32_t covariance_i(int32_t *array1, int32_t *array2, uint32_t n_elements)
{
  if (n_elements == 0) {
    // Note that something else is wrong if you want the covariance of 0 samples.
    return 0;
  }
  // Determine means for each vector:
  float sumX = 0.f, sumY = 0.f, sumXY = 0.f;
 
  // Determine the covariance:
  uint32_t i;
  for (i = 0; i < n_elements; i++) {
    sumX += (float)array1[i];
    sumY += (float)array2[i];
    sumXY += (float)(array1[i]) * (float)(array2[i]);
  }
  return (int32_t)(sumXY / n_elements - sumX * sumY / (n_elements * n_elements));
}
 
/*********
 * Float implementations
 *********/
 
float sum_f(float *array, uint32_t n_elements)
{
  // determine the mean for the vector:
  float sum = 0.f;
  uint32_t i;
  for (i = 0; i < n_elements; i++) {
    sum += array[i];
  }
  return sum;
}
 
float mean_f(float *array, uint32_t n_elements)
{
  if (n_elements == 0) {
    // Note that something else is wrong if you want the mean of 0 samples.
    return 0.f;
  }
  return (sum_f(array, n_elements) / n_elements);
}
 
float variance_f(float *array, uint32_t n_elements)
{
  return covariance_f(array, array, n_elements);
}
 
float covariance_f(float *arr1, float *arr2, uint32_t n_elements)
{
  if (n_elements == 0) {
    // Note that something else is wrong if you want the covariance of 0 samples.
    return 0.f;
  }
  // Determine means for each vector:
  float sumX = 0.f, sumY = 0.f, sumXY = 0.f;
 
  // Determine the covariance:
  uint32_t i;
  for (i = 0; i < n_elements; i++) {
    sumX += arr1[i];
    sumY += arr2[i];
    sumXY += arr1[i] * arr2[i];
  }
  return (sumXY / n_elements - sumX * sumY / (n_elements * n_elements));
}