How to run one command on several cores

I have a command which I want to run on all free cores to speed up the execution time. Specifically I am running the Pitman-Yor Adaptor-Grammar Sampler software I downloaded from here ./py-cfg/py-cfg-mp -r 0 -d 10 -x 10 -D -E -e 1 -f 1 -g 10 -h 0.1 -w 1 -T 1 -m 0 -n 500 -G x.tgt y.tgt < z.tgt I tried adding parallel -j "$(nproc)" before the command as specified in this answer but it is generating the following error: Error in ./py-cfg/py-cfg-mp, argc = 29, optind = 27