Re: Out of memory.

*To*: mathgroup at smc.vnet.net*Subject*: [mg89271] Re: Out of memory.*From*: David Bailey <dave at Remove_Thisdbailey.co.uk>*Date*: Tue, 3 Jun 2008 03:59:11 -0400 (EDT)*References*: <g1tjji$kh9$1@smc.vnet.net> <200806012033.QAA02073@smc.vnet.net> <g20b4e$g0l$1@smc.vnet.net>

Richard Bowles wrote: > Thanks Daniel and David for taking the time to reply. > > I have added a more complete sample of the code, with a simplified > version of the matrix (10x10), that takes the 4th power of the > matrix. This runs in a few mins. It will produce a couple of 1/0 > division errors, but these disappear with increasing matrix size. > > A couple of additional points might also be of help. > > 1. The matrix is algebraic, so I was expecting memory problems with > the MatrixPower operation, but this is actually completed for the full > problem. The out of memory occurs once it has entered the loop for > extracting the coefficients and exponents. The error occurs after a > number of cycles has been completed. I plotted out MemoryInUse[] as a > function of the number of inner loop cycles and see a linear increase > in the memory consumed with one large jump in memory use part way > through. This suggest me that it might be possible to release the > memory consumed at each step but I have been unable to figure out how. > However, there is an Expand[] operation in the loop over all the > elements of the matrix, and this polynomial becomes extremely large > with increasing power and it might be this point that ultimately does > me in rather than the incremental memory consumption of the inner loop. > > 2. The configuration of the machine is correct, but I dont know how > much of this memory Mathematica has access to. > > cheers > Richard > Your code runs in a few seconds (probably mainly notebook I/O time) on my machine - so I think there is something different compared with your machine. My machine is 32-bit, 2GHz, with 1G of main memory! If I print out MemoryInUse[] in the inner loop, it never rises above ~10 MB! BTW, your output streams were a bit tangled up. My guess is one of the following: 1) There is a missing assignment to some variable which makes the algebraic expressions on your side much larger. 2) You auto-execute some other code that accidentally gives a value to something before the code starts to work. NB: You can apply ByteCount to expressions to see how expensive they are. David Bailey http://www.dbaileyconsultancy.co.uk

**References**:**Re: Out of memory.***From:*David Bailey <dave@Remove_Thisdbailey.co.uk>