#include <stdio.h>
#include <mpi.h>
#include <math.h>
#include <string.h>
#include <stdlib.h>
int main(int argc, char * argv[]) {
/*Simple general MPI example*/

/*MPI initialization*/
MPI_Init(&argc,&argv);

/*Initialize "global" variables*/
int root=0; /*The process that will do the receiving and output*/
int isendcount=1; /*How many integers will be gathered*/
/*Get the MPI "locals"*/
int rank;
MPI_Comm_rank(MPI_COMM_WORLD,&rank); /*The process rank*/
char proc_name[MPI_MAX_PROCESSOR_NAME];
int name_len;
MPI_Get_processor_name(proc_name,&name_len); /*The processor name*/

/*Do the initialization, only by the root process*/
int numtasks;
int* irecvbuf;
if (rank==root) {
  MPI_Comm_size(MPI_COMM_WORLD,&numtasks);
  irecvbuf=malloc(numtasks*sizeof(int)); /*Make room for gathering the process ranks*/
}

/*Do "the work" (by all processes)*/
int isendbuf=rank;
int name_len_max;

/*Find out the maximum length of the processor name, accross all processes*/
MPI_Allreduce(&name_len,&name_len_max,isendcount,MPI_INT,MPI_MAX,MPI_COMM_WORLD);

/*Waste some time, so that the program takes a noticeable time to finish*/
int length=100000;
double atmp[length],btmp[length];
for (int i=0; i<length; i++) atmp[i]=(i-1)/((length-1)*1e0);
for (int i=0; i<100; i++) btmp[i]=acos(cos(atmp[i]*acos(-1e0)));
/*End of "the work"*/

/*Make room to get the processor names*/
char* crecvbuf;
if (rank==root) crecvbuf=malloc((name_len_max)*numtasks*sizeof(char));

/*Get the results from everybody*/
MPI_Gather(&isendbuf,isendcount,MPI_INT,irecvbuf,isendcount,MPI_INT,root,MPI_COMM_WORLD);
MPI_Gather(&proc_name,name_len,MPI_CHAR,crecvbuf,name_len,MPI_CHAR,root,MPI_COMM_WORLD);

/*Show the results (only the root process does this)*/
if (rank==root) {
  printf("I am process number %i\n",rank);
  printf("Running on processor %s\n",proc_name);
  printf("Number of tasks is %i\n",numtasks);
  char* name=malloc((name_len_max)*sizeof(char));
  for (int i=0; i<numtasks; i++){
    strncpy(name,crecvbuf+i*(name_len),name_len);
    printf("Process rank %i ran on processor %s\n",irecvbuf[i],name);
  }
}

MPI_Finalize();
return 0;
}