coef_cdf

new function:
1.add new function get_histogram
2.add float
coef_result

1.delete the last line in the txt to make it easy to handle the
coef_result.txt
fix bug reviewFriend_R

fix bugs:
the result of R

1,the png shows the result of the distribution of pairs of friends for a
business
2. most of businesses have few pair fo friends
R_value.docx

1. the word file documents the result of R