Parallel Integration Master
	Some PVM Examples

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <pvm3.h>
#include "func.h"

/* 
 * Find the area to the tolerance.
 */
static double find(double x1, double y1, double x2, double y2, double tol)
{
        /* Compute the midpoint from the funcion. */
        double midx = (x1 + x2) / 2;
        double midy = f(midx);

        /* Estimate the midpoint from the y value. */
        double midest = (y1 + y2) / 2;

        /* See if we're getting close. */
        if(fabs(midy - midest) <= tol)
                /* Will do.  Compute the area using the midy, since we
                   found it.  Two trapazoids algebraically simplified. */
                return 0.25*(x2-x1)*(y1 + y2 + 2*midy);
        else 
                /* Subdivide and try again. */
                return find(x1, y1, midx, midy, tol) +
                        find(midx, midy, x2, y2, tol);
}

#define INITMAX 20

int main(int argc, char **argv)
{
        int cc, tid;

        /* Fine argument whine. */
        if(argc < 5) {
                printf("Usage: %s startx endx tol nreg funcargs*\n", 
                       argv[0]);
                exit(2);
        }

        /* Get the args. */
        char *pname = argv[0];
        double start = atof(argv[1]);
        double end = atof(argv[2]);
        double tol = atof(argv[3]);
        int nreg = atoi(argv[4]);

        argc -= 5; argv += 5;

        if(argc > INITMAX) {
                printf("Function init limited to %d args.\n", INITMAX);
                exit(4);
        }

        /* Sanity. */
        if(tol < 0.0000000001) {
                printf("Tolerance to too small or negative.\n");
                exit(3);
        }
        if(nreg < 1) {
                printf("Number of regions is nonpositive.\n");
                exit(4);
        }
        if(end < start) {
                double t = start;
                start = end;
                end = t;
        }

        int tids[nreg - 1];
        if(nreg > 1) {
                char buf[100];
                strcat(strcpy(buf, pname), "_slave");
                cc = pvm_spawn(buf, 0, 0, "", nreg - 1, tids);
                if(cc <= 0) {
                        /* Nothing was spawned.  Whine about it. */
                        pvm_perror("Spawn failed");
                        pvm_exit();
                        exit(5);
                }

                if(cc != nreg - 1) {
                        /* At least one spawn failed.  Reduce the number
                           of regions to what we could get. */
                        nreg = cc + 1;
                        printf("Unable to spawn all slaves.  Reducing "
                               "to %d regions.\n", nreg);
                }

                /* Send out the function init information. */
                int n;
                pvm_packf("%+ %d", PvmDataDefault,argc);
                for(n = 0; n < argc; n++) {
                        int len = strlen(argv[n]);
                        pvm_pkint(&len, 1, 1);
                        pvm_pkstr(argv[n]);
                }
                pvm_mcast(tids, nreg - 1, 1);
        }

        /* Initialize the function. */
        finit(argc, argv);

        /* Divide into to nreg regions and send all but one of 
           them to each of the slaves. */
        double x = start;
        double inc = (end - start) / nreg;
        int i;
        for(i = 0; i < nreg - 1; ++i) {
                double newx = x + inc;
                pvm_packf("%+ %lf %lf %lf ", 
                          PvmDataDefault, x, newx, tol);
                pvm_send(tids[i], 2);
                x = newx;
        }

        /* Take the last region ourselves. */
        double tot = find(x, f(x), end, f(end), tol);

        /* Collect the others. */
        for(i = 0; i < nreg - 1; ++i) {
                int rn = pvm_recv(-1, 3);
                double portion;
                pvm_upkdouble(&portion, 1, 1);
                tot += portion;
        }

        printf("Integral from %g to %g = %g (tol %g)\n", 
               start, end, tot, tol);

        pvm_exit();
        exit(0);
}