Thank you so much for your suggestions. There are indeed solved the problem.
One more quick question:
My current likelihood is Multinomial. When I set the observation matrix 1 * 62, the program took around 4 minutes, but very very slow when observation matrix is 96 * 62. I checked the time needed of codes before pm.sample(), less than 1 s. I wonder, is my data large or the multinomial is inherently slow? Any suggestions on speeding up?