解决参考 http://askubuntu.com/questions/190246/ld-cannot-find-math-library
you should use -lm at the end.because unresolved symbols are found after gcc encounters montecarlo_time.o and there is no library or anything else in which it can find it can resolve that symbol.
把 -lm 链接发到 -o 前面 ，放到链接其他库的最后面
ubuntu 下 数学库编译链接时找不到各种数学问题解决方法 can not fon atan 等等
原文：http://www.cnblogs.com/yuliyang/p/4370873.html