Re: Add terms surrounded by zero together in matrix

*To*: mathgroup at smc.vnet.net*Subject*: [mg59144] Re: Add terms surrounded by zero together in matrix*From*: "Valeri Astanoff" <astanoff at yahoo.fr>*Date*: Sat, 30 Jul 2005 01:25:18 -0400 (EDT)*References*: <dcccur$3j7$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

I suggest you use Combinatorica and proceed roughly like this (I didn't deal with side effects): In[1]:=<<DiscreteMath`Combinatorica` In[2]:=m={{0,0,0,1,0},{0,0,1,2,0},{0,0,0,2,1},{1,3,0,0,0}, {0,0,0,0,0},{0,0,0,0,0},{0,0,1,1,0}, {5,0,3,0,0},{0,0,0,0,0},{0,0,0,3,1}}; im=Length[m]; jm=Length[m[[1]]]; select non nul vertices : vtx=Outer[List,Range[im],Range[jm]]//Flatten[#,1]&// Select[#,m[[#[[1]],#[[2]]]] != 0&]&; f = function to tell if 2 vertices are connected f[{i1_,j1_},{i1_,j2_/;j2 <= jm}]/;j2 == j1+1:= m[[i1,j1]] != 0 && m[[i1,j1+1]] != 0; f[{i1_,j1_},{i2_/;i2 <= im,j1_}]/;i2 == i1+1:= m[[i1,j1]] != 0 && m[[i1+1,j1]] != 0; [here : more to specify for f ... ] In[8]:=gr=MakeGraph[vtx,f,Type -> Undirected]; In[9]:=ConnectedComponents[gr] Out[9]={{1,2,3,4,5},{6,7},{8,9,11},{10},{12,13}} etc. etc. hth Valeri Astanoff