Probability distribution function

Hi every one
I have a question about calculation of probability distribution function.
How can I coded probability distribution function of chain segmental order parameter?

Your question is quite vague since it is lacking context and specific relevance to a specific LAMMPS simulation and simulation input. It is always difficult to answer such questions accurately in all generality.

You cannot really compute probability distribution functions from simulation data, since you need to discrettize the continuous data into bins to have statistically meaningful results. That can be done with fix ave/histo for distribution over time, and with fix ave/chunk with distribution over space, provided you use a binning method in compute atom/chunk.

Beyond that, all available properties that can be computed are listed in the manual and if you want to compute something that is not listed, you will need to implement it in C++ and information for that you can also consult the manual.