opencv - nvidia 720m and cuda support

Hi guys, is my first post in this forum and i’m sorry for my bad english. I’m trying to write a motion detect programm,in c++, using opencv; when i try to manage a lot of stream in the same time the program became too weighty for my cpu so i want use gpu for execute MOG2 algorithm. From opencv documentation it is compiled whit cuda support and gpu classes use that, but when i try to compile somethings i recieve more errors. The functions cv::gpu::getCudaEnabledDeviceCount() return 0 if there isn’t a device who support cuda ora if opencv is not copilated whit cuda support (im sure that is because i use cmake and i ceck “WHIT_CUDA”) so my vga dosen’t support cuda? Is an 720m.