Vector& SquareMatrix::MPImulVector(const Vector& vector) const {

    double* arr = this->array;
    double result[size];
    double* buffer;
    int amount, rank;

    MPI_Init(&argc, &argv);
    MPI_Comm_size(MPI_COMM_WORLD, &amount);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);

    unsigned lines = size / amount;
    unsigned remLines = size - amount * lines;
    double res[lines];

    if (rank == 0) {

        buffer = arr;
        for (unsigned it = 1; it < amount - 1; ++it)
            MPI_Send(arr + it * lines * size, lines * size, MPI_DOUBLE, it, 0, MPI_COMM_WORLD);
        if (amount > 1)
            MPI_Send(arr + (amount - 1) * lines * size, (lines + remLines) * size, MPI_DOUBLE, amount - 1, 0, MPI_COMM_WORLD);
    }

    else if (rank != amount - 1) {

        double buffer[lines * size];
        MPI_Recv(buffer, lines * size, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
    }

    else {

        lines += remLines;

        double buffer[lines * size];
        MPI_Recv(buffer, lines * size, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
    }

    for (unsigned it = 0; it != lines; ++it)
        res[it] = 0;

    for (unsigned it = 0; it != lines; ++it)
        for (unsigned j = 0; j != size; ++j)
            res[it] += buffer[it * size + j] * vector[j];

    if (rank != 0) {
        MPI_Send(res, lines, MPI_DOUBLE, 0, 1, MPI_COMM_WORLD);
    }

    else {

        for (unsigned it = 0; it != lines; ++it)
            result[it] = res[it];

        for (unsigned it = 1; it < amount - 1; ++it)
            MPI_Recv(result + it * lines, lines, MPI_DOUBLE, it, 1, MPI_COMM_WORLD, MPI_STATUS_IGNORE);

        if (amount > 1)
            MPI_Recv(result + (amount - 1) * lines, lines + remLines, MPI_DOUBLE, amount - 1, 1, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
    }

    Vector& New = *(new Vector(result, size));
    MPI_Finalize();
    return New;
}