MPI scatterv gatherv

Question

在下面的（简化）代码中，我有一个类，其第一个成员是指向指针的指针（动态矩阵），我想知道如何使用scatterv和gatherv。我的目标是使用指向行的指针“水平”分割矩阵。

类：

#include <iostream>

using namespace std;

class Mat{

private:

int **m;
unsigned cols;
unsigned rows;

void allocate_mem(int ***ptr, unsigned r, unsigned c){
    *ptr = new int *[r];
    (*ptr)[0] = new int[r*c];
    for(unsigned i = 1; i < r; i++)
        (*ptr)[i] = (*ptr)[0] + i*c;
}

public:

Mat(){
    rows = 1;
    cols = 1;
    allocate_mem(&m, 1, 1);
    m[0][0] = 0;
}

Mat(unsigned n_rows, unsigned n_cols){
    rows = n_rows;
    cols = n_cols;
    allocate_mem(&m, rows, cols);
        for(unsigned i = 0; i < rows; i++)
            for(unsigned j = 0; j < cols; j++)
                m[i][j] = i+j;
}

Mat &operator=(const Mat &mrx){
    int **new_ptr = NULL;
    allocate_mem(&new_ptr, mrx.rows, mrx.cols);
    for(unsigned i = 0; i < mrx.rows; i++)
        for(unsigned j = 0; j < mrx.cols; j++)
            new_ptr[i][j] = mrx[i][j];
    delete[] m[0];
    delete[] m;
    m = new_ptr;
    rows = mrx.rows;
    cols = mrx.cols;
    return *this;
}

const int *operator[](unsigned n) const{
    return m[n];
}

void create_output(){
    for(unsigned i = 0; i < cols; i++){
        for(unsigned j = 0; j < rows; j++){
            cout << m[i][j] << "\t";
        }
        cout << "\n";
    }
}

~Mat(){
    delete[] m[0];
    delete[] m;
}

};

主：

#include "Mat.cpp"
#include <mpi.h>
#include <iostream>

using namespace std;

int main(int argc, char **argv){

MPI_Init(&argc, &argv);

int rank;
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
int p;
MPI_Comm_size(MPI_COMM_WORLD, &p);

Mat m;

if(rank==0){
    m = Mat(10,10);
    cout << "First:" << endl;
    m.create_output();
}

MPI_Barrier(MPI_COMM_WORLD);

//MPI_Scatterv();

//MPI_Gatherv();

if(rank==0){
    cout << "Second:" << endl;
    m.create_output();
}

MPI_Finalize();

return 0;

}