// This slave process will take the first and last values in a domain and
// calculate a chunk of Gregory's Formula. If the numbers are a and b, it
// calculates +/- [1/a - 1/(a+2) + 1/(a+4) - ...] until 1/b is reached.
// It then sends the result back to the master (aka 'da masta').

#include <stdio.h>
#include "/usr/local/pvm3/include/pvm3.h"

int main()
{
  int mytid, nproc, who;
  int master, msgtype;
  double tempsum;
  long i, sign;
  unsigned long first, last;

  // Enroll in PVM
  mytid = pvm_mytid();

  // Receive data from master
  msgtype = 314;
  pvm_recv(-1, msgtype);
  // Get task ID number and first and last value in range
  pvm_upkint(&who, 1, 1);
  pvm_upklong(&first, 1, 1);
  pvm_upklong(&last, 1, 1);

  // Start with odd numbers, then find the sign of the first term.
  if (first % 2 == 0) first++;
  if (sign % 4 == 1) sign = -4;
  else sign = 4;
  // Initialize partial sum to 0, then go ahead with the formula.
  tempsum = 0;
  for (i = first; i < last; i += 2)
  {
    tempsum += (double)sign / (double)i;
    sign *= -1;
  }

  // Send data back to master
  pvm_initsend(PvmDataDefault);
  pvm_pkint(&who, 1, 1);
  pvm_pkdouble(&tempsum, 1, 1);
  msgtype = 2718;
  master = pvm_parent();
  pvm_send(master, msgtype);

  // Exit PVM, then exit the program.
  pvm_exit();

  return 0;
}

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