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MathGroup Archive 2000

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Re: Could this be improved?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg21772] Re: Could this be improved?
  • From: axc at gamow.ces.cwru.edu
  • Date: Thu, 27 Jan 2000 22:56:53 -0500 (EST)
  • Organization: Case Western Reserve University
  • References: <86mdpv$2f3@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

slightly more compact:

In[1]:=
v = {1, 2, 3, 4}
 
Out[1]=
{1, 2, 3, 4}
 
In[2]:=
totlen = 2*Length[v] - 1; 
 
In[2]:=
w = Join[Table[0, {totlen - Length[v]}], Reverse[v], 
   Table[0, {totlen - Length[v]}]]
 
Out[3]=
{0, 0, 0, 4, 3, 2, 1, 0, 0, 0}
 
In[4]:=
Table[Take[w, {k, k + Length[v] - 1}], {k, totlen, 1, -1}]
 
Out[4]=
{{1, 0, 0, 0}, {2, 1, 0, 0}, {3, 2, 1, 0}, {4, 3, 2, 1}, 
   {0, 4, 3, 2}, {0, 0, 4, 3}, {0, 0, 0, 4}}

 
alan calvitti
systems & control engr
case western reserve university



"Jordan Rosenthal" <jr at ece.gatech.edu> writes:
> 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 ]



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