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https://github.com/mihakralj/QuanTAlib.git
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Add R² and SMAPE error metrics with comprehensive tests and documentation
- Introduced R² (Coefficient of Determination) metric with detailed mathematical foundation, performance profile, and usage examples. - Implemented SMAPE (Symmetric Mean Absolute Percentage Error) metric, addressing asymmetry in MAPE with symmetric error calculations. - Added unit tests for SMAPE covering various scenarios including edge cases and input validation. - Enhanced Dema class to correctly handle event publishing with isNew parameter. - Updated Quantower test project to include coverage configuration for better test reporting.
This commit is contained in:
Miha Kralj
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using System.Runtime.CompilerServices;
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using System.Runtime.InteropServices;
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namespace QuanTAlib;
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/// <summary>
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/// MAPD: Mean Absolute Percentage Deviation
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/// </summary>
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/// <remarks>
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/// MAPD measures the average absolute percentage deviation between actual and predicted values.
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/// Unlike MAPE which divides by actual, MAPD divides by predicted.
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///
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/// Formula:
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/// MAPD = (100/n) * Σ|((actual - predicted) / predicted)|
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///
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/// Key properties:
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/// - Scale-independent (expressed as percentage)
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/// - Cannot be calculated when predicted = 0
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/// - Differs from MAPE in denominator choice
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/// - More stable when actuals have high variance
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/// </remarks>
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[SkipLocalsInit]
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public sealed class Mapd : AbstractBase
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{
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private readonly RingBuffer _buffer;
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[StructLayout(LayoutKind.Auto)]
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private record struct State(double Sum, double LastValidActual, double LastValidPredicted, int TickCount);
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private State _state;
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private State _p_state;
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private const int ResyncInterval = 1000;
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public Mapd(int period)
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{
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if (period <= 0)
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throw new ArgumentException("Period must be greater than 0", nameof(period));
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_buffer = new RingBuffer(period);
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Name = $"Mapd({period})";
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WarmupPeriod = period;
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}
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public override bool IsHot => _buffer.IsFull;
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public TValue Update(TValue actual, TValue predicted, bool isNew = true)
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{
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double actualVal = actual.Value;
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double predictedVal = predicted.Value;
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if (!double.IsFinite(actualVal))
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actualVal = double.IsFinite(_state.LastValidActual) ? _state.LastValidActual : 0.0;
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else
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_state.LastValidActual = actualVal;
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if (!double.IsFinite(predictedVal))
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predictedVal = double.IsFinite(_state.LastValidPredicted) ? _state.LastValidPredicted : 1.0; // Avoid division by zero
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else
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_state.LastValidPredicted = predictedVal;
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// Avoid division by zero - use small epsilon if predicted is zero
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double divisor = Math.Abs(predictedVal) < 1e-10 ? 1e-10 : predictedVal;
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double percentageError = 100.0 * Math.Abs((actualVal - predictedVal) / divisor);
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if (isNew)
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{
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_p_state = _state;
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double removedValue = _buffer.Count == _buffer.Capacity ? _buffer.Oldest : 0.0;
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_state.Sum = _state.Sum - removedValue + percentageError;
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_buffer.Add(percentageError);
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_state.TickCount++;
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if (_buffer.IsFull && _state.TickCount >= ResyncInterval)
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{
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_state.TickCount = 0;
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_state.Sum = _buffer.RecalculateSum();
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}
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}
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else
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{
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_state = _p_state;
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double removedValue = _buffer.Count == _buffer.Capacity ? _buffer.Oldest : 0.0;
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_state.Sum = _state.Sum - removedValue + percentageError;
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_buffer.UpdateNewest(percentageError);
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_state.Sum = _buffer.RecalculateSum();
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}
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double result = _buffer.Count > 0 ? _state.Sum / _buffer.Count : percentageError;
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Last = new TValue(actual.Time, result);
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PubEvent(Last, isNew);
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return Last;
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}
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public TValue Update(double actual, double predicted, bool isNew = true)
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{
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return Update(new TValue(DateTime.UtcNow, actual), new TValue(DateTime.UtcNow, predicted), isNew);
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}
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public override TValue Update(TValue input, bool isNew = true)
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{
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throw new NotSupportedException("MAPD requires two inputs. Use Update(actual, predicted).");
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}
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public override TSeries Update(TSeries source)
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{
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throw new NotSupportedException("MAPD requires two inputs. Use Calculate(actualSeries, predictedSeries, period).");
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}
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public override void Prime(ReadOnlySpan<double> source, TimeSpan? step = null)
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{
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throw new NotSupportedException("MAPD requires two inputs.");
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}
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public override void Reset()
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{
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_buffer.Clear();
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_state = default;
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_p_state = default;
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Last = default;
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}
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public static TSeries Calculate(TSeries actual, TSeries predicted, int period)
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{
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if (actual.Count != predicted.Count)
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throw new ArgumentException("Actual and predicted series must have the same length", nameof(predicted));
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int len = actual.Count;
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var t = new List<long>(len);
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var v = new List<double>(len);
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CollectionsMarshal.SetCount(t, len);
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CollectionsMarshal.SetCount(v, len);
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var tSpan = CollectionsMarshal.AsSpan(t);
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var vSpan = CollectionsMarshal.AsSpan(v);
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Batch(actual.Values, predicted.Values, vSpan, period);
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actual.Times.CopyTo(tSpan);
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return new TSeries(t, v);
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}
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static void Batch(ReadOnlySpan<double> actual, ReadOnlySpan<double> predicted, Span<double> output, int period)
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{
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if (actual.Length != predicted.Length || actual.Length != output.Length)
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throw new ArgumentException("All spans must have the same length", nameof(output));
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if (period <= 0)
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throw new ArgumentException("Period must be greater than 0", nameof(period));
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int len = actual.Length;
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if (len == 0) return;
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const int StackAllocThreshold = 256;
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Span<double> buffer = period <= StackAllocThreshold
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? stackalloc double[period]
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: new double[period];
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double sum = 0;
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double lastValidActual = 0;
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double lastValidPredicted = 1.0; // Default to 1 to avoid division by zero
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for (int k = 0; k < len; k++)
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{
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if (double.IsFinite(actual[k])) { lastValidActual = actual[k]; break; }
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}
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for (int k = 0; k < len; k++)
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{
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if (double.IsFinite(predicted[k]) && Math.Abs(predicted[k]) >= 1e-10) { lastValidPredicted = predicted[k]; break; }
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}
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int bufferIndex = 0;
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int i = 0;
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int warmupEnd = Math.Min(period, len);
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for (; i < warmupEnd; i++)
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{
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double act = actual[i];
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double pred = predicted[i];
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if (double.IsFinite(act)) lastValidActual = act; else act = lastValidActual;
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if (double.IsFinite(pred) && Math.Abs(pred) >= 1e-10) lastValidPredicted = pred; else pred = lastValidPredicted;
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double divisor = Math.Abs(pred) < 1e-10 ? 1e-10 : pred;
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double percentageError = 100.0 * Math.Abs((act - pred) / divisor);
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sum += percentageError;
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buffer[i] = percentageError;
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output[i] = sum / (i + 1);
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}
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int tickCount = 0;
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for (; i < len; i++)
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{
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double act = actual[i];
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double pred = predicted[i];
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if (double.IsFinite(act)) lastValidActual = act; else act = lastValidActual;
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if (double.IsFinite(pred) && Math.Abs(pred) >= 1e-10) lastValidPredicted = pred; else pred = lastValidPredicted;
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double divisor = Math.Abs(pred) < 1e-10 ? 1e-10 : pred;
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double percentageError = 100.0 * Math.Abs((act - pred) / divisor);
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sum = sum - buffer[bufferIndex] + percentageError;
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buffer[bufferIndex] = percentageError;
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bufferIndex++;
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if (bufferIndex >= period) bufferIndex = 0;
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output[i] = sum / period;
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tickCount++;
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if (tickCount >= ResyncInterval)
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{
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tickCount = 0;
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double recalcSum = 0;
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for (int k = 0; k < period; k++) recalcSum += buffer[k];
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sum = recalcSum;
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}
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}
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}
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}
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