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  1. #include <array>
  2. #include <deque>
  3. #include <cmath>
  4. #include <stdexcept>
  5.  
  6. // ── Configuration ────────────────────────────────────────────────
  7. static constexpr int NUM_SENSORS = 4;
  8.  
  9. // ── Types ────────────────────────────────────────────────────────
  10.  
  11. // One timestep: one scalar reading per sensor
  12. struct SensorFrame {
  13.     std::array<double, NUM_SENSORS> values;
  14. };
  15.  
  16. // Sliding window of the N most recent frames
  17. using SensorWindow = std::deque<SensorFrame>;
  18.  
  19. // ── Core: push a new frame, keeping window size <= N ─────────────
  20.  
  21. void push_frame(SensorWindow& window, const SensorFrame& frame, int N) {
  22.     if (N <= 0) throw std::invalid_argument("N must be positive");
  23.     window.push_back(frame);
  24.     while (static_cast<int>(window.size()) > N)
  25.         window.pop_front();
  26. }
  27.  
  28. // ── Geometric mean of all values across the entire window ────────
  29. //
  30. // Treats every scalar in the window (all sensors × all timesteps)
  31. // as one flat list and returns the Nth-root product, where
  32. // N = window_size × NUM_SENSORS.
  33. //
  34. // Uses the log-sum trick to avoid overflow/underflow.
  35.  
  36. double geometric_mean_all(const SensorWindow& window) {
  37.     if (window.empty()) throw std::runtime_error("Window is empty");
  38.  
  39.     double log_sum = 0.0;
  40.     int    count   = 0;
  41.  
  42.     for (const auto& frame : window) {
  43.         for (double v : frame.values) {
  44.             if (v <= 0.0)
  45.                 throw std::domain_error("Geometric mean requires positive values");
  46.             log_sum += std::log(v);
  47.             ++count;
  48.         }
  49.     }
  50.  
  51.     return std::exp(log_sum / count);
  52. }
  53.  
  54. // ── Per-sensor geometric mean across the window ──────────────────
  55. //
  56. // Returns one geometric mean per sensor channel, computed over
  57. // the N timesteps in the window.
  58.  
  59. std::array<double, NUM_SENSORS>
  60. geometric_mean_per_sensor(const SensorWindow& window) {
  61.     if (window.empty()) throw std::runtime_error("Window is empty");
  62.  
  63.     std::array<double, NUM_SENSORS> log_sums{};
  64.     log_sums.fill(0.0);
  65.  
  66.     for (const auto& frame : window) {
  67.         for (int s = 0; s < NUM_SENSORS; ++s) {
  68.             if (frame.values[s] <= 0.0)
  69.                 throw std::domain_error("Geometric mean requires positive values");
  70.             log_sums[s] += std::log(frame.values[s]);
  71.         }
  72.     }
  73.  
  74.     std::array<double, NUM_SENSORS> result{};
  75.     double n = static_cast<double>(window.size());
  76.     for (int s = 0; s < NUM_SENSORS; ++s)
  77.         result[s] = std::exp(log_sums[s] / n);
  78.  
  79.     return result;
  80. }
  81.  
  82. int main() {
  83.     const int N = 5;          // keep last 5 measurements
  84.     SensorWindow window;
  85.  
  86.     // Simulate incoming sensor readings
  87.     push_frame(window, {{ 1.2, 3.4, 2.1, 0.9 }}, N);
  88.     push_frame(window, {{ 1.5, 3.1, 2.4, 1.0 }}, N);
  89.     push_frame(window, {{ 1.1, 3.6, 2.0, 1.2 }}, N);
  90.  
  91.     // Global geometric mean (single pseudo-fusion scalar)
  92.     double global = geometric_mean_all(window);
  93.  
  94.     // Per-sensor geometric mean (one value per sensor)
  95.     auto per_sensor = geometric_mean_per_sensor(window);
  96.  
  97.     return 0;
  98. }
Success #stdin #stdout 0.01s 5288KB
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https://ideone.com/6ZDR4m
language:
C++ (gcc 8.3)
created:
12 hours ago
visibility:
public

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