Re: Intensive numerical calculations

*To*: mathgroup at smc.vnet.net*Subject*: [mg80595] Re: Intensive numerical calculations*From*: Cristian <LumisrobTogliquesto at yahoo.com>*Date*: Sun, 26 Aug 2007 23:08:02 -0400 (EDT)*References*: <f9s445$all$1@smc.vnet.net><fabgog$id8$1@smc.vnet.net> <fae9u4$ec7$1@smc.vnet.net> <200708220838.EAA08507@smc.vnet.net> <faj4vu$8sk$1@smc.vnet.net> <200708240557.BAA16587@smc.vnet.net> <far8u8$3r6$1@smc.vnet.net>

On Sun, 26 Aug 2007 07:08:56 +0000 (UTC), Daniel Lichtblau <danl at wolfram.com> wrote: >Cristian wrote: >> On Thu, 23 Aug 2007 05:12:30 +0000 (UTC), Daniel Lichtblau >> <danl at wolfram.com> wrote: >> >> >>>Cristian wrote: >> >> ]zac[ >> >>>Suffice it to say that a dense representation will cause problems for >>>most software on many machines. As for a sparse represntation, and >>>computational speed, it will depend on what specifically you want to do. >>>Mathematica uses some fairly good libraries for certain linear algebra >>>operations on such matrices. If what you require is not well supported >>>then you might need to go to some other approach, perhaps via MathLink. >>> >>>Daniel Lichtblau >>>Wolfram Research >>> >> >> My problem is not the dimension of the matrixes. Certainly the >> limitation on the packeds array (< 2^31)limits, but my true problem is >> the slowness in to pass these matrixes to the form c++ by matlink. >> That that profit inserting pieces in c++, I lose in the transfers >> through matlink. I have to develop a form (structural fem) >> personalized for the analysis of parts mechanics submitted to dynamic >> solicitations and I was considering mathematica because I knew it from >> the university. If I use c++ and MTL for example it'is ok There is a >> method for move more quickly big matrixes (unfortunately the matrixes >> become full with the progress of the footsteps and it would be for me >> too complicated to avoid this to the beginning) from Mathematica to >> an external form in c++? > > >If you provide simple examples and take the trouble to use correct >terminology then you will more likely get useful responses. Thanks > For example, >there is no "matlink" (the program you have in mind, I suspect, is >MathLink). Yes MATHLINK I apologize for the error >>Moreover you still have not specified what is your data >format when it resides in Mathematica. SparseArray[...]? Something else? > >Maybe what you will require is some form of Export. I believe that >function supports some matrix types but it is, as I note, unclear which >would be appropriate, as you gave no example. > >As for matrix fill-in, I'd be really surprised if your C++ library code >uses a dense method for solving linear systems of the sort generated for >FEM, with dimension around 10^5. I have never said to have to resolve a linear system. What you have in mind ( I suspect), it is a wrong hypothesis >As noted in a prior response, that >would be close to 100 Gb, and that is a large chunk of memory to work >with. Not to mention time, since you would likely have an O(n^3) >algorithm, or at best maybe O(n^2.4) or so from asymptotically fastest >approaches to matrix multiplication. This to my notice is wrong. There are methodologies that reduce the order of calculation ("Matrix Computation" Golub/ Van Loan or "Accuracy and stab..." Higham) > >Much more likely is that a Krylov type of method would be used. Similar >to what Mathematica might do in solving a sparse system using machine >double arithmetic. > > >Daniel Lichtblau >Wolfram Research > However thanks for the availability. I now have however definite to continue with the c++ and every doubt of mine I will turn t on the NGs of such language Thanks Cristian

**References**:**Re: Intensive numerical calculations***From:*Cristian <LumisrobTogliquesto@yahoo.com>

**Re: Intensive numerical calculations***From:*Cristian <LumisrobTogliquesto@yahoo.com>