# Changes

## GPU610/Team AGC

, 21:36, 24 November 2014
1-D Wave Equation
[[Image:wave2.gif]]

The first step was to create a private repository on Bitbucket to avoid any plagerism issues with this course for next semester students, as well as provide code revision and protection in case my progress is lost or corrupt.

The next step is to convert the following C file into C++ code that will be compatible with CUDA.

mpi_wave.c
<pre>
/***************************************************************************
* FILE: mpi_wave.c
* OTHER FILES: draw_wave.c
* DESCRIPTION:
* MPI Concurrent Wave Equation - C Version
* Point-to-Point Communications Example
* This program implements the concurrent wave equation described
* in Chapter 5 of Fox et al., 1988, Solving Problems on Concurrent
* Processors, vol 1.
* A vibrating string is decomposed into points. Each processor is
* responsible for updating the amplitude of a number of points over
* time. At each iteration, each processor exchanges boundary points with
* nearest neighbors. This version uses low level sends and receives
* to exchange boundary points.
* AUTHOR: Blaise Barney. Adapted from Ros Leibensperger, Cornell Theory
* Center. Converted to MPI: George L. Gusciora, MHPCC (1/95)
* LAST REVISED: 07/05/05
***************************************************************************/
#include "mpi.h"
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define MASTER 0
#define TPOINTS 800
#define MAXSTEPS 10000
#define PI 3.14159265

int RtoL = 10;
int LtoR = 20;
int OUT1 = 30;
int OUT2 = 40;

void init_master(void);
void init_workers(void);
void init_line(void);
void update (int left, int right);
void output_master(void);
void output_workers(void);
extern void draw_wave(double *);

numtasks, /* number of processes */
nsteps, /* number of time steps */
npoints, /* number of points handled by this processor */
first; /* index of 1st point handled by this processor */
double etime, /* elapsed time in seconds */
values[TPOINTS+2], /* values at time t */
oldval[TPOINTS+2], /* values at time (t-dt) */
newval[TPOINTS+2]; /* values at time (t+dt) */

/* ------------------------------------------------------------------------
* Master obtains timestep input value from user and broadcasts it
* ------------------------------------------------------------------------ */
void init_master(void) {
char tchar;

/* Set number of number of time steps and then print and broadcast*/
nsteps = 0;
while ((nsteps < 1) || (nsteps > MAXSTEPS)) {
printf("Enter number of time steps (1-%d): \n",MAXSTEPS);
scanf("%s", tchar);
nsteps = atoi(tchar);
if ((nsteps < 1) || (nsteps > MAXSTEPS))
printf("Enter value between 1 and %d\n", MAXSTEPS);
}
MPI_Bcast(&nsteps, 1, MPI_INT, MASTER, MPI_COMM_WORLD);
}

/* -------------------------------------------------------------------------
* Workers receive timestep input value from master
* -------------------------------------------------------------------------*/
void init_workers(void) {
MPI_Bcast(&nsteps, 1, MPI_INT, MASTER, MPI_COMM_WORLD);
}

/* ------------------------------------------------------------------------
* All processes initialize points on line
* --------------------------------------------------------------------- */
void init_line(void) {
int nmin, nleft, npts, i, j, k;
double x, fac;

/* calculate initial values based on sine curve */
fac = 2.0 * PI;
for (i = 0, k = 0; i < numtasks; i++) {
npts = (i < nleft) ? nmin + 1 : nmin;
first = k + 1;
npoints = npts;
first, npts);
for (j = 1; j <= npts; j++, k++) {
x = (double)k/(double)(TPOINTS - 1);
values[j] = sin (fac * x);
}
}
else k += npts;
}
for (i = 1; i <= npoints; i++)
oldval[i] = values[i];
}

/* -------------------------------------------------------------------------
* All processes update their points a specified number of times
* -------------------------------------------------------------------------*/
void update(int left, int right) {
int i, j;
double dtime, c, dx, tau, sqtau;
MPI_Status status;

dtime = 0.3;
c = 1.0;
dx = 1.0;
tau = (c * dtime / dx);
sqtau = tau * tau;

/* Update values for each point along string */
for (i = 1; i <= nsteps; i++) {
/* Exchange data with "left-hand" neighbor */
if (first != 1) {
MPI_Send(&values, 1, MPI_DOUBLE, left, RtoL, MPI_COMM_WORLD);
MPI_Recv(&values, 1, MPI_DOUBLE, left, LtoR, MPI_COMM_WORLD,
&status);
}
/* Exchange data with "right-hand" neighbor */
if (first + npoints -1 != TPOINTS) {
MPI_Send(&values[npoints], 1, MPI_DOUBLE, right, LtoR, MPI_COMM_WORLD);
MPI_Recv(&values[npoints+1], 1, MPI_DOUBLE, right, RtoL,
MPI_COMM_WORLD, &status);
}
/* Update points along line */
for (j = 1; j <= npoints; j++) {
/* Global endpoints */
if ((first + j - 1 == 1) || (first + j - 1 == TPOINTS))
newval[j] = 0.0;
else
/* Use wave equation to update points */
newval[j] = (2.0 * values[j]) - oldval[j]
+ (sqtau * (values[j-1] - (2.0 * values[j]) + values[j+1]));
}
for (j = 1; j <= npoints; j++) {
oldval[j] = values[j];
values[j] = newval[j];
}
}
}

/* ------------------------------------------------------------------------
* Master receives results from workers and prints
* ------------------------------------------------------------------------ */
void output_master(void) {
int i, j, source, start, npts, buffer;
double results[TPOINTS];
MPI_Status status;
/* Store worker's results in results array */
for (i = 1; i < numtasks; i++) {
/* Receive first point, number of points and results */
MPI_Recv(buffer, 2, MPI_INT, i, OUT1, MPI_COMM_WORLD, &status);
start = buffer;
npts = buffer;
MPI_Recv(&results[start-1], npts, MPI_DOUBLE, i, OUT2,
MPI_COMM_WORLD, &status);
}

/* Store master's results in results array */
for (i = first; i < first + npoints; i++)
results[i-1] = values[i];

j = 0;
printf("***************************************************************\n");
printf("Final amplitude values for all points after %d steps:\n",nsteps);
for (i = 0; i < TPOINTS; i++) {
printf("%6.2f ", results[i]);
j = j++;
if (j == 10) {
printf("\n");
j = 0;
}
}
printf("***************************************************************\n");
printf("\nDrawing graph...\n");
printf("Click the EXIT button or use CTRL-C to quit\n");

/* display results with draw_wave routine */
draw_wave(&results);
}

/* -------------------------------------------------------------------------
* Workers send the updated values to the master
* -------------------------------------------------------------------------*/
void output_workers(void) {
int buffer;
MPI_Status status;

/* Send first point, number of points and results to master */
buffer = first;
buffer = npoints;
MPI_Send(&buffer, 2, MPI_INT, MASTER, OUT1, MPI_COMM_WORLD);
MPI_Send(&values, npoints, MPI_DOUBLE, MASTER, OUT2, MPI_COMM_WORLD);
}

/* ------------------------------------------------------------------------
* Main program
* ------------------------------------------------------------------------ */

int main (int argc, char *argv[])
{
int left, right, rc;

/* Initialize MPI */
MPI_Init(&argc,&argv);
printf("Need at least 2 tasks! Quitting...\n");
MPI_Abort(MPI_COMM_WORLD, rc);
exit(0);
}

/* Determine left and right neighbors */
right = 0;
else

else

/* Get program parameters and initialize wave values */
printf ("Using %d points on the vibrating string.\n", TPOINTS);
init_master();
}
else
init_workers();

init_line();

/* Update values along the line for nstep time steps */
update(left, right);

/* Master collects results from workers and prints */