Description 
Implementation details of (i)(iii) can be found in [1].
The fourth function (gmm2sv.m) is to concatenate the means (i.e. centers) of GMM. The concatenated mean of adapted GMM is known as GMM supervector (GSV) and it is used in GMMSVM based speaker recognition system. Details of GMMSVM based speaker recognition system can be found in [2].
These codes require Netlab toolbox.
http://www1.aston.ac.uk/eas/research/groups/ncrg/resources/netlab/
References:
[1] D. A. Reynolds, T. F. Quatieri, and R. B. dunn, "Speaker verification using adapted Gaussian mixture models", Digital signal processing, vol. 10, pp. 1941, 2000.
[2] Campbell, W.M.; Sturim, D.E.; Reynolds, D.A.; , "Support vector machines using GMM supervectors for speaker verification," Signal Processing Letters, IEEE , vol.13, no.5, pp. 308 311, May 2006.
