Re: Calling functions with huge arguments
- To: mathgroup at smc.vnet.net
- Subject: [mg97657] Re: Calling functions with huge arguments
- From: ragfield <ragfield at gmail.com>
- Date: Wed, 18 Mar 2009 04:52:42 -0500 (EST)
- References: <gpns8b$gkh$1@smc.vnet.net>
On Mar 17, 4:58 am, Fernando Cucchietti <fernando.cucchie... at icfo.es> wrote: > 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? I don't know whether this solves your problem or not, but you can sort of fake "pass by reference" behavior by giving your subroutine a Hold* (HoldAll/HoldFirst/HoldRest) attribute. This way the subroutine has access to the symbol you pass in and it can make changes in place. In[1]:= Attributes[MyFunc] = HoldAll; In[2]:= MyFunc[a_Symbol] := (a[[2]] = 2.2); In[3]:= b = {1., 2., 3., 4.} Out[3]= {1., 2., 3., 4.} In[4]:= MyFunc[b]; In[5]:= b Out[5]= {1., 2.2, 3., 4.} -Rob