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这几天在两台机器上跑lammps,偶然发现分别跑了两个一样的算例,但结果却有不一样,后来查了下手册,发现12.1 Common problems中写了如下一段话:
If two LAMMPS runs do not produce the exact same answer on different machines or different numbers of processors, this is typically not a bug. In theory you should get identical answers on any number of processors and on any machine. In practice, numerical round-off can cause slight differences and eventual divergence of molecular dynamics phase space trajectories within a few 100s or few 1000s of timesteps. However, the statistical properties of the two runs (e.g. average energy or temperature) should still be the same.
个人理解,瞬时量没有太大意义,做某个时间段的平均更有统计意义。
下面摘自lammps mailing test关于这种问题一个答复:
“you are comparing apples with oranges, i.e. numbers that have been averaged over 99 steps each 5 steps apart, with numbers from a single step. why *should* they be the same?”
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