matlab问题：tic，toc是什么东西，怎么用的

tic， s=0; for i=1:100000， s=s+1/2^i+1/3^i; end; toc 这样的一个语句，为什么每次的到的结果不同 Elapsed time is 0.189000 seconds. Elapsed time is 0.210000 seconds. Elapsed time is 0.196000 seconds. Elapsed time is 0.203000 seconds. Elaps... tic， s=0; for i=1:100000， s=s+1/2^i+1/3^i; end; toc 这样的一个语句，为什么每次的到的结果不同 Elapsed time is 0.189000 seconds. Elapsed time is 0.210000 seconds. Elapsed time is 0.196000 seconds. Elapsed time is 0.203000 seconds. Elapsed time is 0.197000 seconds. Elapsed time is 0.205000 seconds. Elapsed time is 0.199000 seconds. Elapsed time is 0.199000 seconds. Elapsed time is 0.189000 seconds.