Use of actInv() in frameClassicAcceleration of TSID

[xiaosuyang]

Hello.
In the tsid robotwrapper.cpp, function RobotWrapper::frameClassicAcceleration() which is used to calculate the classic accleration of a frame:

In row 301 and 302, a and v are spatial acc and spatial vel of the frame f, but why they use placement.actInv(data.v[f.parent])(data.v[f.parent] is the vel of the parent joint ) instead of placement.act(). Isn't the frameXJoint.act() used to transform the vector from Joint coordinate to the frame coordinate?

[stephane-caron]

Since this question is related to TSID, you should ask it in the TSID discussions forum.