Is there any formal generalization of the needlman-wunsch algorithm to 3 dimensions instead of pairwise alignment ? I've searched a lot but couldn't find enough details for example I scanned the book "biological sequence alignment " for R. Durbin but I need more details : 1- how to initialize the 3d matrix 2- how to fill the matrix 3- how to score ( I know the sum of pairs method) but if there is a complete example it'll be clearer 4- how to trace back

Thanks in advance for either explaining my points or giving any resource or example