After this commad : mpiexec -n 5 -f machinefile ./examples/cpi, it has some errors when run, errors like :

 HYDU_parse_hostfile (/home/mojtaba/libraries/mpich-3.1/src/pm/hydra/utils/args/args.c:319): unable to open host file: machinefile
[mpiexec@Mojtaba] mfile_fn (/home/mojtaba/libraries/mpich-3.1/src/pm/hydra/ui/mpich/utils.c:336): error parsing hostfile
[mpiexec@Mojtaba] match_arg (/home/mojtaba/libraries/mpich-3.1/src/pm/hydra/utils/args/args.c:152): match handler returned error
[mpiexec@Mojtaba] HYDU_parse_array (/home/mojtaba/libraries/mpich-3.1/src/pm/hydra/utils/args/args.c:174): argument matching returned error
[mpiexec@Mojtaba] parse_args (/home/mojtaba/libraries/mpich-3.1/src/pm/hydra/ui/mpich/utils.c:1596): error parsing input array
[mpiexec@Mojtaba] HYD_uii_mpx_get_parameters (/home/mojtaba/libraries/mpich-3.1/src/pm/hydra/ui/mpich/utils.c:1648): unable to parse user arguments
[mpiexec@Mojtaba] main (/home/mojtaba/libraries/mpich-3.1/src/pm/hydra/ui/mpich/mpiexec.c:153): error parsing parameters

what is the problem?

thanks,

-- 
Mojtaba S. Moghani
Faculty of Environment
University of Tehran