Re: Calling functions with huge arguments

*To*: mathgroup at smc.vnet.net*Subject*: [mg97688] Re: Calling functions with huge arguments*From*: dh <dh at metrohm.com>*Date*: Wed, 18 Mar 2009 04:58:35 -0500 (EST)*References*: <gpns8b$gkh$1@smc.vnet.net>

Hi Fernando, with the attribute HoldFirst or HoldAll, you can prevent evaluation of the argument.If you specify a symbol in the function call, the function receives the symbol. Take care, inside the function the symbol is evaluated if needed. Here is an example for pass-by-reference. a is changed afterwards: Clear[fun]; SetAttributes[fun, HoldFirst]; fun[large_, small_] := large = large + small; a = 1; b = 2; fun[a, b] a hope this helps, Daniel Fernando Cucchietti wrote: > Hi all, > > I am working with a VERY large tensor, so much that I would like to > keep at most two copies of it in memory at any given time. The > algorithm I want to run is convoluted and repetitive, but it looks > very compact when written in terms of subroutines and functions that > call themselves many times. However, from what I gather, Mathematica > effectively creates a copy of the arguments when a function is called. > Is this correct? > If so, I need to find a way to mimic pass-by-reference style as in C > or Fortran, or just pass the arguments that are not big and keep my > tensors defined globally (which I think makes the code look less > nice). Unwrapping the code so that it does not call functions is not > an option, because it would be very complex and never-again-usable. > My main question is then: what are the best ways to do pass-by- > reference (if it is better than global naming), or what approaches > have you taken to overcome similar problems? > > Thanks in advance, > > Fernando >