Change GPU Fan Speed NVIDIA API

I search the NVIDIA Api to change the GPU Fan Speed.
Read the docs nvapi,nvml and nvcpl but don’t find the function to change the speed.

Can someone help me?

Have now found the informations:

http://code.google.com/p/open-hardware-monitor
http://eliang.blogspot.ch/2011/05/getting-nvidia-gpu-usage-in-c.html

My fault, don’t see this before.
Can’t understand why its not official documented, but based on my informations, it is so?!

what about controlling the fan speed in c++?