I am a little unclear on the mean update formula used in HMap.c

This line in HMap.c UpdateMeans

mean[k] = ( mean[k] * mapTau + (ma->mu[k] + mean[k]*occim) )/( mapTau + occim );

seems to differ from the MAP update formula (Section 9.3, eqn 9.8)
shown in HTKBook?

Assuming,
mean[k] -> prior mean
mapTau -> backoff weight
ma->mu[k] -> first-order stats from adaptation data
occim -> occupation stats from adaptation data

The extra-term seems to be "mean[k]*occim". Can someone clarify this?

And,the parameter mapTau's value ,how should i adjust this value ?  

Thanks,

Nick

--- (Edited on 10/3/2014 11:40 am [GMT-0500] by clyou2014) ---

--- (Edited on 10/3/2014 11:43 am [GMT-0500] by clyou2014) ---