Re: Could this be improved?

*To*: mathgroup at smc.vnet.net*Subject*: [mg21769] Re: [mg21741] Could this be improved?*From*: Bojan Bistrovic <bojanb at physics.odu.edu>*Date*: Thu, 27 Jan 2000 22:56:50 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

> Hi all, > > I wrote the following code which works correctly. I was wondering, however, > if there was a way of doing the same thing that had more of a Mathematica > approach. I am new to Mathematica and am still trying to get a grasp on how > to program effectively within the environment. > > myMtx[v_] := Module[ > {nCols, nRows, vPadded, c}, > nCols = Length[v]; > nRows = 2nCols - 1; > c = ZeroMatrix[nRows, nCols]; > vPadded = PadRight[v, nRows, 0]; > For[i = 1, i <= nCols, i++, > c[[All, i]] = vPadded; > vPadded = RotateRight[vPadded] > ]; > c > ] > > For example, myMtx[{1,2,3}] takes the vector {1,2,3} and turns it into the > matrix {{1, 0, 0}, {2, 1, 0}, {3, 2, 1}, {0, 3, 2}, {0, 0, 3}} which looks > like > > [ 1 0 0 ] > [ 2 1 0 ] > [ 3 2 1 ] > [ 0 3 2 ] > [ 0 0 3 ] > > > Thanks, > > Jordan > Here's one: myMtx[v_List]:= Table[Take[ Drop[Join[Table[0,{kk,1,2 Length[v]-jj}],Reverse[v], Table[0,{kk,1,jj}]],Length[v]-1],Length[v]],{jj,2Length[v] ,2,-1}] or this one (which is faster) myMtx2[v_List]:= Join[Table[ Table[ PadRight[Take[Reverse[v],-kk],Length[v]],{kk,1,Length[v]}]], Reverse[Table[ Table[PadLeft[Take[Reverse[v],kk],Length[v]],{kk,1,Length[v]-1}]]]] Bye, bojan ------------------------------------------------------------- Bojan Bistrovic, bojanb at physics.odu.edu Old Dominion University, Physics Department, Norfolk, VA -------------------------------------------------------------