cvFindStereoCorrespondenceGC(), disparityLeft / disparityRight

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I'm using the graph-cuts cvFindStereoCorrespondenceGC() function:

void cvFindStereoCorrespondenceGC(const CvArr *left, const CvArr *right, CvArr *disparityLeft, CvArr *disparityRight, CvStereoGCState *state, int useDisparityGuess = 0).

My question is: what is the disparityLeft and disparityRight maps that I am supposed to get?

Shouldn't there only be one disparity map like what cvFindStereoCorrespondenceBM() gives you?

cvFindStereoCorrespondenceBM(const CvArr *left, const CvArr *right, CvArr *disparity, CvStereoBMState *state)