$ mpirun -np 4 pirules
Process number 0 on processor voyager.umsl.edu 

Which rule do you want to use?
 0= done 
 1=rectangular rule 
 2=mid point rule
 3=simpsons rule 
 Process number 1 on processor compute-0-0.local 
Process number 2 on processor compute-0-1.local 
Process number 3 on processor compute-0-2.local 
1

Please input the number of intervals(0 quits).
10000000

pi is approximately 3.1415927535898307, Relative Error is   3.18310006e-06
wall clock time = 0.116112

Which rule do you want to use?
 0= done 
 1=rectangular rule 
 2=mid point rule
 3=simpsons rule 
 2

Please input the number of intervals(0 quits).
10000000

pi is approximately 3.1415926535897607, Relative Error is  -1.03191330e-12
wall clock time = 0.163527

Which rule do you want to use?
 0= done 
 1=rectangular rule 
 2=mid point rule
 3=simpsons rule 
 3

Please input the number of intervals(0 quits).
10000000

pi is approximately 3.1415926535897611, Relative Error is  -1.01777750e-12
wall clock time = 0.328525

Which rule do you want to use?
 0= done 
 1=rectangular rule 
 2=mid point rule
 3=simpsons rule 
 3

Please input the number of intervals(0 quits).
1000

pi is approximately 3.1415926535897931, Relative Error is   0.00000000e+00
wall clock time = 0.000408

Which rule do you want to use?
 0= done 
 1=rectangular rule 
 2=mid point rule
 3=simpsons rule 
 0
[siegelj@voyager solidcode]$ mpirun -np 8 pirules
Process number 0 on processor voyager.umsl.edu 

Which rule do you want to use?
 0= done 
 1=rectangular rule 
 2=mid point rule
 3=simpsons rule 
 Process number 6 on processor compute-0-1.local 
Process number 5 on processor compute-0-0.local 
Process number 4 on processor compute-0-3.local 
Process number 7 on processor compute-0-2.local 
Process number 2 on processor compute-0-1.local 
Process number 3 on processor compute-0-2.local 
Process number 1 on processor compute-0-0.local 
1

Please input the number of intervals(0 quits).
10000000

pi is approximately 3.1415927535897907, Relative Error is   3.18309879e-06
wall clock time = 0.115095

Which rule do you want to use?
 0= done 
 1=rectangular rule 
 2=mid point rule
 3=simpsons rule 
 0
$ mpirun -np 2 pirules
Process number 0 on processor voyager.umsl.edu

Which rule do you want to use?
 0= done
 1=rectangular rule
 2=mid point rule
 3=simpsons rule
 Process number 1 on processor compute-0-0.local
1

Please input the number of intervals(0 quits).
10000000

pi is approximately 3.1415927535897517, Relative Error is   3.18309754e-06
wall clock time = 0.230361

Which rule do you want to use?
 0= done
 1=rectangular rule
 2=mid point rule
 3=simpsons rule
 0
$