Re: copying values of entries between matrices
- To: mathgroup at smc.vnet.net
- Subject: [mg77984] Re: copying values of entries between matrices
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Thu, 21 Jun 2007 05:32:39 -0400 (EDT)
- Organization: The Open University, Milton Keynes, UK
- References: <f5atd0$an9$1@smc.vnet.net>
text.tex wrote:
> Hi,
> here is my problem:
> I have a 18x18 matrix called entMatr.
> I want to copy the values of the elements of the lower left half of
> entMatr into a 171x1 matrix called dOneCol.
> I had tried a 3-nested loop for copying the values from entMatr to
> dOneCol; the current version where I tried to replace the loop over
> the rows of dOneCol with a counter q produces a result, however the
> result is not what I want...
>
> I'd greatly appreciate any pointers how to get this working!
> Thanks,
> Claus
>
> This is what I tried:
>
> <pre>
> (* initialize entMatr *)
> entMatr = Table[Subscript[m, i, j], {i, 18}, {j, 18}];
>
> (* fill the lower left half of entMatr with some values *)
> For[i = 1, i < 18 + 1, i++,
> For[j = i, j < 18 + 1, j++,
> entMatr[[j, i]] = i
> ]
> ]
>
> (* initialize dOneCol *)
> dOneCol = Table[Subscript[n, x], {x, 171}];
>
> (* attempt to copy the values from entMatr to dOneCol *)
> q = 0;
> For[k = 1, k < 18 + 1, k++,
> For[p = k, p < 18 + 1, p++,
> dOneCol[[q]] = entMatr[[p,k]]
> q++
> ]
> ]
> dOneCol
> </pre>
Assuming I have correctly understood what you wanted, one way of doing
that is the following:
dOneCol =
Reap[Do[If[j <= i, Sow[entMatr[[i, j]]]], {i, 18}, {j, 18}]][[2, 1]]
For instance,
entMatr = Array[Subscript[m, ##1] & , {18, 18}];
For[i = 1, i < 18 + 1, i++, For[j = i, j < 18 + 1, j++,
entMatr[[j, i]] = i]]
MatrixForm[entMatr]
dOneCol =
Reap[Do[If[j <= i, Sow[entMatr[[i, j]]]], {i, 18}, {j, 18}]][[
2, 1]]
Length[dOneCol]
MatrixForm[dOneCol]
Regards,
Jean-Marc