Re: Creating a symmetric matrix
- To: mathgroup at smc.vnet.net
- Subject: [mg46961] Re: Creating a symmetric matrix
- From: Paul Abbott <paul at physics.uwa.edu.au>
- Date: Thu, 18 Mar 2004 01:24:44 -0500 (EST)
- Organization: The University of Western Australia
- References: <c2p9ld$dns$1@smc.vnet.net> <200403130440.XAA15145@smc.vnet.net> <A8166766-7689-11D8-A63D-0003938BF55C@jeol.com> <c36baq$s26$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
In article <c36baq$s26$1 at smc.vnet.net>, DrBob <drbob at bigfoot.com> wrote: > Building a matrix that large (2000x2000), when half the information is > redundant, is probably a bad idea in the first place; and that applies to > the upper-triangular matrix you're taking it from as well. > > Instead, you should write code that uses the necessary information more > efficiently. > > SparseArray also may be of help. Perhaps something like Flatten[Table[{i,j} -> a[i,j],{j, 1, 4}, {i, 1, j}]]; % /. ({i_, j_} -> a_) :> {j, i} -> a; Normal[SparseArray[Join[%, %%]]] Cheers, Paul -- Paul Abbott Phone: +61 8 9380 2734 School of Physics, M013 Fax: +61 8 9380 1014 The University of Western Australia (CRICOS Provider No 00126G) 35 Stirling Highway Crawley WA 6009 mailto:paul at physics.uwa.edu.au AUSTRALIA http://physics.uwa.edu.au/~paul
- References:
- Re: Creating a symmetric matrix
- From: drbob@bigfoot.com (Bobby R. Treat)
- Re: Creating a symmetric matrix