contact less smart thermometer

C:\Users\admin\AppData\Local\Temp\ccvtCDfb.ltrans0.ltrans.o: In function `global constructors keyed to 65535_0_csir_thermometer.ino.cpp.o.2015':

e:\Documents\Arduino\csir_thermometer/csir_thermometer.ino:7: undefined reference to `MLX90615::MLX90615(unsigned char)'

C:\Users\admin\AppData\Local\Temp\ccvtCDfb.ltrans0.ltrans.o: In function `setup':

e:\Documents\Arduino\csir_thermometer/csir_thermometer.ino:14: undefined reference to `MLX90615::begin()'

C:\Users\admin\AppData\Local\Temp\ccvtCDfb.ltrans0.ltrans.o: In function `loop':

e:\Documents\Arduino\csir_thermometer/csir_thermometer.ino:35: undefined reference to `MLX90615::get_object_temp()'

e:\Documents\Arduino\csir_thermometer/csir_thermometer.ino:46: undefined reference to `MLX90615::get_object_temp()'

collect2.exe: error: ld returned 1 exit status

exit status 1

Error compiling for board Arduino/Genuino Uno.

this is the error i am facing please help sir