Using implicit information about row indices
- To: mathgroup at smc.vnet.net
- Subject: [mg68254] Using implicit information about row indices
- From: "Diamond, Mark" <dot at dot.dot>
- Date: Mon, 31 Jul 2006 03:45:06 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
I am wanting to fill a square matrix M (say, r by r) using information from
a list, L.
The list L is also of length r, but is not a square matrix. It contains
lists of ordered pairs {col, num}
It typically looks something like this; I have arranged it into rows so that
it is more obvious
{
{{1, a}, {2, b}},
{{1, c}, {2, d}, {3, e}, {4, f}},
{{2, g}, {3, h}, {4, i}},
{{3, k}, {4, l}, {5,m}},
{{4, n}, {5, p}}
}
Now what I am trying to do is, for example, set M[[1,1]]=a, M[[1,2]]=b,
M[[2,1]]=c, M[[2.2]]=d, M[[2,3]]=e and so forth, and leave (or set) all the
other entries in M to zero. The row information for M is implicit in the
structure of the list L; additionally, the column indices as they appear
within sublist of L are guraranteed to be sequential. It seems with all this
info, there should be an easy way to fill M correctly, but I have struggled
without success to do anything other than an iterative process with Do[]. I
would appreciate any guidance you might have.
Thank you.
Mark Diamond