Re: Re: ack! simple partitioning problem making my head swim....
- To: mathgroup at smc.vnet.net
- Subject: [mg42110] Re: [mg42079] Re: [mg42050] ack! simple partitioning problem making my head swim....
- From: Bobby Treat <drmajorbob-MathGroup3528 at mailblocks.com>
- Date: Thu, 19 Jun 2003 03:59:41 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
1) The result of matrix multiplication doesn't have to be square, as
that condition would require.
2) cdj isn't used matrices that are formatted as matrices, so that
condition won't work for him at all.
Bobby
-----Original Message-----
From: Tomas Garza <tgarza01 at prodigy.net.mx>
To: mathgroup at smc.vnet.net
Subject: [mg42110] [mg42079] Re: [mg42050] ack! simple partitioning problem
making my head swim....
Perhaps this will help. If the following is True, then you can multiply
list1.list2, otherwise you can't.
In[1]:=
Dimensions[list1] == Reverse[Dimensions[list2]]
Tomas Garza
Mexico City
----- Original Message -----
From: "cdj" <a_cjones at hotmail.com>
To: mathgroup at smc.vnet.net
Subject: [mg42110] [mg42079] [mg42050] ack! simple partitioning problem making my
head
swim....
> Hi all,
>
> I'm given 2 (ordered) lists - list1 has elements a_1,..a_n, and list2
> has elements b_1,...,b_n.
>
> As efficiently as possible, I want to determine whether or not these
> lists represent matrices that can be multiplied together. In list
> format, I'm imagining that "a list represents a matrix" means simply:
> the 1st row of the matrix are the first list entries, the second row
> comes next, and so on (just as in the Mathematica command
> Flatten[{{1,2},{3,4}}] = {1,2,3,4}.
>
> (a) It's clear enough that finding a solution to this problem is gonna
> involve comparing the factors in the lengths of the two lists, but
> then it all goes wishywashy in my head. lil help?
>
> (b) Assume there does exist a way of partitioning the two input lists
> so that they form "multiplicatively-friendly" matrices. Is this
> guaranteed to be unique? Or is it possible that there be *several*
> ways to partition given lists into m-friendly matrices?
>
> thanks a bunch for any insights,
>
> cdj
>
>