namespace DTS.Common.Calculations
{
    public static class Integral
    {
        /// <summary>
        /// integrates a channel over an interval
        /// </summary>
        /// <param name="input">data to integrate</param>
        /// <param name="start">index to start integration at (inclusive)</param>
        /// <param name="end">index to end integration at (inclusive)</param>
        /// <returns></returns>
        public static double DefiniteIntegral(double[] input, int start, int end, double SPS)
        {
            //we use trapezoidal summation to get integral, there is an assumption that the input data is 
            //tightly time aligned (otherwise we'd have to divide each interval by the actual distance, and not 1/2)
            //=(SUMPRODUCT(H25:H56,A26:A57)-SUMPRODUCT(A25:A56,H26:H57)+A57*H57-A25*H25)/2
            double d = 0;
            for (int i = start + 1; i < end; i++)
            {
                d += 2D * input[i];
            }
            d += input[start];
            d += input[end];

            return .5D * d / SPS;
        }
    }
}