Difference between revisions of "CSC352 Homework 4 Solutions"

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=Problem 3=
 
=Problem 3=
 +
<br />
 +
A good program by Danae for the MPI question.  Note the use of '''perworker''' and '''permanager''' to make sure the total number of samples adds up ''exactly'' to '''numsamples'''.  Nice touch.
 
<br />
 
<br />
 
<source lang="C">
 
<source lang="C">
 +
[352a@beowulf 352a-aa]$ cat mpiMonteCarlo4.c
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/* mpiMonteCarlo4.c
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// danae
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//
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// Computes Pi using the Monte Carlo method with MPI,
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// NP (user-specified) processes, and N random samples.
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// Note that N should be evenly divisible by NP in order
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// to truly calculate N samples.
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//
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// To compile and run:
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// mpicc -o mpiMonteCarlo4 mpiMonteCarlo4.c
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// mpirun -np [NP] ./mpiMonteCarlo [N]
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//
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*/
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 +
#include "mpi.h"
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#include <stdio.h>
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#include <stdlib.h>
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#define MANAGER 0
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//--------------------------------------------------------------------
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//                        P R O T O T Y P E S
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//--------------------------------------------------------------------
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void doManager(int,int);
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void doWorker();
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//--------------------------------------------------------------------
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//                          M  A  I  N
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//--------------------------------------------------------------------
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int main(int argc, char *argv[]) {
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  int myId, noProcs, nameLen;
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  char procName[MPI_MAX_PROCESSOR_NAME];
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  int numsamples;
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 +
  if ( argc<2 ) {
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    printf( "Please Use Correct Syntax: mpirun -np [NP] ./pi2 [N]\n" );
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    return 1;
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  }
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  // get the number of samples to generate
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  numsamples = atoi(argv[1]);
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  //--- start MPI ---
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  MPI_Init(&argc, &argv);
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  MPI_Comm_rank(MPI_COMM_WORLD, &myId);
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  MPI_Comm_size(MPI_COMM_WORLD, &noProcs);
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  MPI_Get_processor_name(procName, &nameLen);
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  //--- display which process we are on ---
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  printf( "Process %d of %d started.\n", myId,  noProcs);
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  //--- farm out the work: 1 manager, several workers ---
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  if ( myId == MANAGER )
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    doManager(noProcs, numsamples);
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  else
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    doWorker();
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  //--- close up MPI ---
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  MPI_Finalize();
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  return 0;
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}
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//--------------------------------------------------------------------
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// The manager's main work function
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//--------------------------------------------------------------------
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void doManager(int noProcs, int numsamples ) {
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  double incircle = 0;
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  double workersum;
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  int i;
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  MPI_Status status;
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  int perworker = (1.0)*numsamples/noProcs;
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  int permanager = numsamples - perworker*noProcs; //manager picks up slack
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  // printf("perworker: %d\n", perworker);
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  //--- first to all workers ---
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  for(i=1; i<noProcs; i++) {
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    MPI_Send( &perworker, 1, MPI_INT, i, 0, MPI_COMM_WORLD );
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  }
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  //calculate manager portion
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  srand(time(NULL)); //seed the random number generator with time
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  float x, y;
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  for(i=0; i<permanager+perworker; i++) {
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    x = 1 - (((float)rand()/(float)(RAND_MAX)) * 2.0); //random float [-1,1]
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    y = 1 - (((float)rand()/(float)(RAND_MAX)) * 2.0); //random float [-1,1]
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    if ((float)x*x + (float)y*y <= (float)(1.0)) {
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      incircle += 1;
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    }
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  }
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  //--- wait for worker sums ---
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  for(i=1; i<noProcs; i++) {
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    MPI_Recv( &workersum, 1, MPI_DOUBLE, MPI_ANY_SOURCE, 0, MPI_COMM_WORLD, &status );
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    incircle += workersum;
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  }
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  //--- output result ---
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  printf( "%d iterations: Pi = %f\n", permanager + noProcs*perworker, 4.0*(incircle)/(noProcs*perworker));
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}
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 +
//--------------------------------------------------------------------
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// The worker's main work function
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//--------------------------------------------------------------------
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void doWorker( ) {
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  int numthrows, i;
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  //--- get n from manager ---
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  MPI_Status status;
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  MPI_Recv( &numthrows, 1, MPI_INT, MPI_ANY_SOURCE, 0, MPI_COMM_WORLD, &status );
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 +
  //--- do portion of the work ---
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  double incircle = 0;
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  float x, y;
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  for (i=0; i<numthrows; i++) {
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    // generate random x, y as float [0,2], subtracts 1 to be in range [-1,1]
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    x = 1 - (((float)rand()/(float)(RAND_MAX)) * 2.0); //random float [-1,1]
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    y = 1 - (((float)rand()/(float)(RAND_MAX)) * 2.0); //random float [-1,1]
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    if ((float)x*x + (float)y*y <= (float)(1.0))
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      incircle += 1;
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  }
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  //-- send result to manager ---
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  MPI_Send( &incircle, 1, MPI_DOUBLE, MANAGER, 0, MPI_COMM_WORLD );
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}
 +
  
 
</source>
 
</source>

Latest revision as of 15:46, 8 November 2013

--D. Thiebaut (talk) 14:41, 8 November 2013 (EST)



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