Re: matrix operations
- To: mathgroup at smc.vnet.net
- Subject: [mg46361] Re: matrix operations
- From: "Peter Pein" <no at spam.no>
- Date: Mon, 16 Feb 2004 09:00:07 -0500 (EST)
- References: <c0mohe$65t$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
"paolo tarpanelli" <tarpanelli at libero.it> schrieb im Newsbeitrag news:c0mohe$65t$1 at smc.vnet.net... > If I have a matrix > > a={x[[1,1]],x[[1,2]],...,x[[1,n]]} > {x[[2,1]],x[[2,2]],...,x[[2,n]]} > . > . > . > {x[[m,1]],x[[m,2]],...,x[[m,n]]} > > how can I compute the difference between any element and the previous for each column : > > aa={x[[2,1]]-x[[1,1]], x[[2,2]]-x[[1,2]],...,x[[2,n]]-x[[1,n]]} > {x[[3,1]]-x[[2,1]], x[[3,2]]-x[[2,2]],...,x[[3,n]]-x[[2,n]]} > . > . > . > {x[[m,1]]-x[[m-1,1]],x[[m,2]]-x[[m-1,2]],...,x[[m,n]]-x[[m-1,n]]} > > -------------------------------------------------------------------------- ---------------------------- > > I built this code but it does not work > > r=Array[0,{m,n}] > For[j=1,j=n,j++ > r[[i,j]]=Table[a[[i+1,j]]-a[[i,j]],{i,1,m-1,1}]] > > thanks > > Paolo > > ---------------- Hi Paolo, In[1]:= n=3; m=5; a=Table[x[i,j],{i,1,m},{j,1,n}]; In[3]:= a[[Range[2,m]]] - a[[Range[m-1]]] Out[3]= {{-x[1, 1] + x[2, 1], -x[1, 2] + x[2, 2], -x[1, 3] + x[2, 3]}, {-x[2, 1] + x[3, 1], -x[2, 2] + x[3, 2], -x[2, 3] + x[3, 3]}, {-x[3, 1] + x[4, 1], -x[3, 2] + x[4, 2], -x[3, 3] + x[4, 3]}, {-x[4, 1] + x[5, 1], -x[4, 2] + x[5, 2], -x[4, 3] + x[5, 3]}} gives the desired result, as Table[a[[i+1,j]]-a[[i,j]],{i,1,m-1,1},{j,1,n}] does. -- Peter Pein, Berlin petsie at arcAND.de replace && by || to write to me