кв метод

class A
    {
        public static int V = 12;
        static int n = 30;
        class Program
        {

            public static void Main(string[] args)
            {
                double begin = 0;
                double end = 12;

                double part = end - begin;
                part /= n - 1;
                double[] x = new double[n];
                double[][] a = new double[n][];
                for (int i = 0; i < n; i++)
                    a[i] = new double[n];
                double[] b = new double[n];
                x[0] = begin;

                for (int i = 1; i < n; i++)
                {
                    x[i] = x[i - 1] + part;
                }

                double[] yt = new double[n];
                for (int i = 0; i < n; i++)
                {
                    yt[i] = Math.Pow(x[i], 2) + V;
                }
                double h = Math.Abs(x[0] - x[1]);
                for (int i = 0; i < n; i++)
                {
                    for (int j = 0; j < n; j++)
                    {
                        if (j == 0 || j == n - 1)
                        {
                            if (i == j)
                                a[i][j] = 1 + (h * getA(x[i], x[j])) / 2.0;
                            else a[i][j] = (h * getA(x[i], x[j])) / 2.0;
                        }
                        else
                        {
                            if (i == j)
                                a[i][j] = 1 + h * getA(x[i], x[j]);
                            else
                                a[i][j] = h * getA(x[i], x[j]);
                        }
                    }
                }
                for (int i = 0; i < n; i++)
                {
                    b[i] = getF(x[i]);
                }

                double[] y = gaussMethod(a, b);

                print(x, "Значения x:");
                print(yt, "Y точное");
                print(y, "Y");

                Console.WriteLine("Точность");
                for (int i = 0; i < y.Length; i++)
                    Console.Write("{0:F5} | ", Math.Abs(y[i] - yt[i]));

            }

            public static double getF(double x)
            {
                return Math.Pow(x, 2) + V + x * (Math.Pow(V, 4) / 4 + Math.Pow(V, 3) / 2
                        + x * Math.Pow(V, 5) / 5 + x * Math.Pow(V, 4) / 3 + x * x * Math.Pow(V, 6) / 6 + x * x * Math.Pow(V, 5) / 4);

            }

            public static double getA(double x, double t)
            {
                return x * t + Math.Pow(x, 2) * Math.Pow(t, 2) + Math.Pow(x, 3) * Math.Pow(t, 3);
            }

            public static double[] gaussMethod(double[][] a, double[] b)
            {
                for (int i = 0; i < n; i++)
                {
                    if (a[i][i] == 0)
                    {
                        if (!swap(a, b, i))
                        {
                            return new double[n];
                        }
                    }
                    b[i] /= a[i][i];
                    if (a[i][i] != 1)
                    {
                        divide(a[i], a[i][i]);
                    }
                    for (int j = i + 1; j < n; j++)
                    {
                        double s = a[j][i] / a[i][i];
                        if (a[i][j] - s != a[i][j])
                        {
                            for (int k = 0; k < a[i].Length; k++)
                            {
                                a[j][k] -= a[i][k] * s;
                            }
                            b[j] -= b[i] * s;
                        }
                    }
                }
                for (int i = 0; i < n; i++)
                {
                    for (int j = n - i; j < n; j++)
                    {
                        b[n - i - 1] -= b[j] * a[n - i - 1][j];
                    }
                }
                return b;
            }

            public static void divide(double[] line, double value)
            {
                for (int i = 0; i < line.Length; i++)
                {
                    line[i] /= value;
                }
            }

            public static bool swap(double[][] a, double[] b, int index)
            {
                for (int i = index; i < n; i++)
                {
                    if (a[i][index] != 0)
                    {
                        int swapIndex = index;
                        int j = index;
                        double element = a[index][index];
                        while (j < b.Length)
                        {
                            if (element < Math.Abs(a[j][index]))
                            {
                                element = Math.Abs(a[j][index]);
                                swapIndex = j;
                            }
                            j++;
                        }
                        if (swapIndex == n)
                        {
                            break;
                        }
                        double[] tmpRow = a[index];
                        a[index] = a[swapIndex];
                        a[swapIndex] = tmpRow;

                        double tmp = b[index];
                        b[index] = b[swapIndex];
                        b[swapIndex] = tmp;
                        return true;
                    }
                }
                for (int i = index; i < n; i++)
                {
                    if (a[index][i] != 0)
                    {
                        int swapIndex = index;
                        double element = a[index][index];
                        int j = index;
                        while (j < n)
                        {
                            if (element < Math.Abs(a[index][j]))
                            {
                                element = Math.Abs(a[index][j]);
                                swapIndex = j;
                            }
                            j++;
                        }
                        if (swapIndex == n)
                        {
                            break;
                        }

                        for (int k = 0; k < n; k++)
                        {
                            double tmp = a[k][index];
                            a[k][index] = a[k][swapIndex];
                            a[k][swapIndex] = tmp;
                        }
                    }
                    return true;
                }
                return false;
            }

            public static void print(double[] array, String str)
            {
                Console.WriteLine("\n {0}", str);
                foreach (double i in array)
                    Console.Write("{0:F5} | ", i);



            }
        }
    }
}