/home/wWTHI5/cclXxbEJ.o: In function `main':
prog.cpp:(.text+0x16): undefined reference to `Simulator::Simulator()'
/home/wWTHI5/cclXxbEJ.o:(.rodata._ZTI5Kutta[typeinfo for Kutta]+0x8): undefined reference to `typeinfo for Method'
/home/wWTHI5/cclXxbEJ.o:(.rodata._ZTI5Euler[typeinfo for Euler]+0x8): undefined reference to `typeinfo for Method'
collect2: ld returned 1 exit status