参考：https://www.biostars.org/p/106291/#106344
1、inner mate distance : the distance from the right most end of the left read to the left most end of the right read
2、the "insert size"=sequence between adapters (actually encompasses R1 and R2 as well as the unknown gap between them) and it is also known that the ninth column of the SAM file (TLEN) represents the insert size
3.1、Insert size = 400
Library = 2x150bp
Inner size = 400-2*150 = 100
3.2、So for a 2x100bp library with 193 mean insert, your inner distance is 193-2x100 = -7 (meaning that they overlap by 7bp)
4、
Insert_size = the sequence betwwn adapters
Fragment_size= Insert_size + Adapters
