Dear Mohamed : The link above is a good description of this method. And you may solve online the differential equation of interest . THe tool : Maxima software by William Schelter. The yamwi (yet another maxima web interface) is here :
http://maxima.cesga.es/
In order to apply the method you must know the way a recurrence equation is solved by Maxima. See the manual online here : http://maxima.sourceforge.net/docs/manual/de/maxima_70.html