Matrix.Column C# (CSharp) Method

    public int[] Column(int col)
    {
        throw new NotImplementedException("You need to implement this function.");
    }
}

 private static Matrix<double> ComputeMatrixCrossproduct(Matrix<double> matrix, IList<int> columnIndexes)
 {
     var result = new DenseMatrix(columnIndexes.Count, columnIndexes.Count);
     for (int iRow = 0; iRow < columnIndexes.Count; iRow++)
     {
         for (int iCol = 0; iCol < columnIndexes.Count; iCol++)
         {
             result[iRow, iCol] = matrix.Column(columnIndexes[iRow]).DotProduct(matrix.Column(columnIndexes[iCol]));
         }
     }
     return result;
 }