variance_kernel.c

/* * Copyright (c) 2014, 2015                                          Zhang Xianyi
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * * Redistributions of source code must retain the above copyright notice, this
 *   list of conditions and the following disclaimer.
 *
 * * Redistributions in binary form must reproduce the above copyright notice, this
 *   list of conditions and the following disclaimer in the documentation and/or
 *   other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
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#include "openvml_kernel.h"
#include <math.h>

#ifndef DOUBLE
#define VARIANCE variancef
#else
#define VARIANCE variance
#endif

double KERNEL_NAME(VMLLONG n, VML_FLOAT * a, VML_FLOAT * b, VML_FLOAT * y, VML_FLOAT * z, VML_FLOAT * other_params) {
  if (n <= 1 || a == NULL) return NAN;

  double sum = 0.0f;
  for (int i = 0; i < n; i++) {
      sum += a[i];
  }
  double mean = sum / n;

  double variance = 0.0f;
  for (int i = 0; i < n; i++) {
    double diff = a[i] - mean;
      variance += diff * diff;
  }
  return variance / (n - 1);
}