issue with LinearSolve when using SparseArray when size close
- To: mathgroup at smc.vnet.net
- Subject: [mg113622] issue with LinearSolve when using SparseArray when size close
- From: "Nasser M. Abbasi" <nma at 12000.org>
- Date: Fri, 5 Nov 2010 05:11:00 -0500 (EST)
- Reply-to: nma at 12000.org
There is some serious problem I am getting when trying to use
Mathematica LinearSolve to solve Au=f when using SparseArray when the
size of non-zero elements gets close to 1 GB.
The non-zero elements in A that I am building is of the order n^3.
Therefore, for n=255, memory needed should be around 130 Mega Bytes
(255^2*8) (using 8 bytes for each value, I am using numerical everything).
For n=511, memory used should be a little over 1 Giga Bytes.
I have 8 GB Ram. Windows 7, new Intel CPU.
When I run the solver for n=31 or 63 or 127 or 255, it all works, and
Mathematica is fast solving Au=f, takes few seconds, and no problem.
These are the CPU times reported by Mathemtica Timing command for the
n=511, been running for many hrs, memory problem.
When I changed to n=511, I see memory of the Mathematica Kernel going up
to almost 100% of the PC memory, using almost 7 GB, and I have waited
for 9 hrs, and Mathematica is still not done.
There seems, on the face of it, something really wrong here. It seems
SparseArray behavior or how LinearSolve uses it, does not scale well
at all? or is this a windows OS issue? if it is a bug in my code, but it
works so well for all the other n values?
I am posting the code, it is really small code, to see if someone can
please try it on their PC and see if they get the same behavior.
------------ code -----------------
(* make sparse A*)
(* f(x,y) *)
(*n=127; h=2^-7;*) (*these values are OK *)
(*n=255; h=2^-8;*) (*these values are OK *)
n=511; h=2^-9; (*these cause problem *)
(* fill in f vector, in correct order for problem*)
Print["before solver, MemoryInUse=",MemoryInUse];
Print["after solver, MemoryInUse=",MemoryInUse];
Print["after solver, cpu=",cpu];
---------------- end code -----------------
Prev by Date:
Re: Finding only the real roots
Next by Date:
Re: Fonts, Formats, and examples as learning tools
Previous by thread:
Re: Numerical solution of the heat equation on a disk
Next by thread:
Re: issue with LinearSolve when using SparseArray when size close