added comments to the code

math/realtime_stats.cpp

@@ -1,3 +1,11 @@
+/**
+ * \file
+ * \brief Compute statistics for data entered in rreal-time
+ *
+ * This algorithm is really beneficial to compute statistics on data read in
+ * realtime. For example, devices reading biometrics data. The algorithm is
+ * simple enough to be easily implemented in an embedded system.
+ */
 #include <cmath>
 #include <iostream>
 
@@ -8,31 +16,39 @@
 template <typename T>
 class stats_computer1 {
  public:
-  void new_val(T x) {
-    if (n == 0) K = x;
-    n++;
-    T tmp = x - K;
-    Ex += tmp;
-    Ex2 += tmp * tmp;
-  }
+    /** Constructor
+     * \param[in] x new data sample
+     */
+    void new_val(T x) {
+        if (n == 0) K = x;
+        n++;
+        T tmp = x - K;
+        Ex += tmp;
+        Ex2 += tmp * tmp;
+    }
 
-  double mean() const { return K + Ex / n; }
+    /** return sample mean computed till last sample */
+    double mean() const { return K + Ex / n; }
 
-  double variance() const { return (Ex2 - (Ex * Ex) / n) / (n - 1); }
+    /** return data variance computed till last sample */
+    double variance() const { return (Ex2 - (Ex * Ex) / n) / (n - 1); }
 
-  double std() const { return std::sqrt(this->variance()); }
+    /** return sample standard deviation computed till last sample */
+    double std() const { return std::sqrt(this->variance()); }
 
-  friend std::istream &operator>>(std::istream &input, stats_computer1 &stat) {
-    T val;
-    input >> val;
-    stat.new_val(val);
-    return input;
-  }
+    /** short-hand operator to read new sample from input stream */
+    friend std::istream &operator>>(std::istream &input,
+                                    stats_computer1 &stat) {
+        T val;
+        input >> val;
+        stat.new_val(val);
+        return input;
+    }
 
  private:
-  unsigned int n = 0;
-  double Ex, Ex2;
-  T K;
+    unsigned int n = 0;
+    double Ex, Ex2;
+    T K;
 };
 
 /**
@@ -42,57 +58,70 @@ class stats_computer1 {
 template <typename T>
 class stats_computer2 {
  public:
-  void new_val(T x) {
-    n++;
-    double delta = x - mu;
-    mu += delta / n;
-    double delta2 = x - mu;
-    M += delta * delta2;
-  }
+    /** Constructor
+     * \param[in] x new data sample
+     */
+    void new_val(T x) {
+        n++;
+        double delta = x - mu;
+        mu += delta / n;
+        double delta2 = x - mu;
+        M += delta * delta2;
+    }
 
-  double mean() const { return mu; }
+    /** return sample mean computed till last sample */
+    double mean() const { return mu; }
 
-  double variance() const { return M / n; }
+    /** return data variance computed till last sample */
+    double variance() const { return M / n; }
 
-  double std() const { return std::sqrt(this->variance()); }
+    /** return sample standard deviation computed till last sample */
+    double std() const { return std::sqrt(this->variance()); }
 
-  friend std::istream &operator>>(std::istream &input, stats_computer2 &stat) {
-    T val;
-    input >> val;
-    stat.new_val(val);
-    return input;
-  }
+    /** short-hand operator to read new sample from input stream */
+    friend std::istream &operator>>(std::istream &input,
+                                    stats_computer2 &stat) {
+        T val;
+        input >> val;
+        stat.new_val(val);
+        return input;
+    }
 
  private:
-  unsigned int n = 0;
-  double mu = 0, var = 0, M = 0;
+    unsigned int n = 0;
+    double mu = 0, var = 0, M = 0;
 };
 
+/** Main function */
 int main(int argc, char **argv) {
-  std::cout << "Enter data. Any non-numeric data will terminate the data input."
-            << std::endl;
+    std::cout
+        << "Enter data. Any non-numeric data will terminate the data input."
+        << std::endl;
 
-  stats_computer1<double> stats1;
-  stats_computer2<double> stats2;
+    stats_computer1<float> stats1;
+    stats_computer2<float> stats2;
 
-  while (1) {
-    double val;
-    std::cout << "Enter number: ";
-    std::cin >> val;
-    if (std::cin.fail())  // check for failure to read input. Happens for
-                          // non-numeric data
-      break;
-    stats1.new_val(val);
-    stats2.new_val(val);
-    std::cout << "\tMethod 1:"
-              << "\tMean: " << stats1.mean()
-              << "\t Variance: " << stats1.variance()
-              << "\t Std: " << stats1.std() << std::endl;
-    std::cout << "\tMethod 2:"
-              << "\tMean: " << stats2.mean()
-              << "\t Variance: " << stats2.variance()
-              << "\t Std: " << stats2.std() << std::endl;
-  }
+    while (1) {
+        double val;
+        std::cout << "Enter number: ";
+        std::cin >> val;
 
-  return 0;
+        // check for failure to read input. Happens for
+        // non-numeric data
+        if (std::cin.fail()) break;
+
+        stats1.new_val(val);
+        stats2.new_val(val);
+
+        std::cout << "\tMethod 1:"
+                  << "\tMean: " << stats1.mean()
+                  << "\t Variance: " << stats1.variance()
+                  << "\t Std: " << stats1.std() << std::endl;
+        std::cout << "\tMethod 2:"
+                  << "\tMean: " << stats2.mean()
+                  << "\t Variance: " << stats2.variance()
+                  << "\t Std: " << stats2.std() << std::endl;
+    }
+
+    return 0;
 }