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Re: copying values of entries between matrices
*To*: mathgroup at smc.vnet.net
*Subject*: [mg78013] Re: [mg77952] copying values of entries between matrices
*From*: Curtis Osterhoudt <cfo at lanl.gov>
*Date*: Thu, 21 Jun 2007 05:47:31 -0400 (EDT)
*Organization*: LANL
*References*: <200706200937.FAA10111@smc.vnet.net>
*Reply-to*: cfo at lanl.gov
If you have v. 6 of Mathematica, the function "diagonal" should help you out;
to get a list of the elements you want, try
Diagonal[s, #]&/@Range[-(Length@s) + 1, 0]
Of course, if you want these elements on the same level in your dOneCol,
Flatten@Diagonal[s, #]&/@Range[-(Length@s) + 1, 0]
If you have an earlier version, you could try something like the following
(which I haven't optimized for different types of lists or anything, but
should work for matrix arguments):
takeLowerLeft[mat_]:=Take[mat, {2, Length@mat}, {1, Length@mat - 1}]
snagDiags[mat_] := mat[[#, #]] & /@ Range[Length[mat]]
snagDiags /@ NestList[ takeLowerLeft, dOneCol, Length[dOneCol] -1 ]
Flatten@%
Hope that helps!
C.O.
On Wednesday 20 June 2007 03:37:37 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>
--
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Curtis Osterhoudt
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