Laser Diode의 Threshold Current 계산 알고리즘 - Least Square Method - C#

 

	public double ThresholdCurrent(in double[] Current, in double[] Power, double PowerLow, double PowerHigh)
	{
		double thresholdCurrent = 0;

		try
		{
			int startIndex = Array.FindIndex(Power, x => x >= PowerLow);
			int endIndex = Array.FindIndex(Power, x => x >= PowerHigh);

			var subCurrent = Current.Skip(startIndex).Take(endIndex - startIndex + 1).ToArray();
			var subPower = Power.Skip(startIndex).Take(endIndex - startIndex + 1).ToArray();

			var (slope, intercept) = LeastSquaresFit(subCurrent, subPower);

			if(slope != 0) thresholdCurrent = -intercept / slope;            
		}
		catch
		{
			thresholdCurrent = 0 ;
		}		

		return thresholdCurrent;
	}	
	//-----------------------------------------------------------------------------------------------------------------
	private (double Slope, double Intercept) LeastSquaresFit(double[] x, double[] y)
	{
		int n = x.Length;        
        
        double sumX = x.Sum();
        double sumY = y.Sum();
        double sumXY = x.Zip(y, (xi, yi) => xi * yi).Sum();
        double sumXX = x.Select(xi => xi * xi).Sum();
        
        Slope = (n * sumXY - sumX * sumY) / (n * sumXX - sumX * sumX);
        Intercept = (sumY - Slope * sumX) / n;
		
		return (slope, yIntercept);
	}
	//-----------------------------------------------------------------------------------------------------------------