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MathGroup Archive 2000

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Re : Fast (compiled) routine for element testing and replacement in large matrices? A more general question about Listable

  • To: mathgroup at smc.vnet.net
  • Subject: [mg24000] [mg23978] Re : Fast (compiled) routine for element testing and replacement in large matrices? A more general question about Listable
  • From: Jacqueline Zizi <jazi at club-internet.fr>
  • Date: Mon, 19 Jun 2000 01:45:43 -0400 (EDT)
  • References: <8iccl1$9oj@smc.vnet.net> <200006180701.DAA21625@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Bob Abraham wrote:

> Hi Gareth ---
>
> This way should be much faster:
>
> d2wreal[w_, l_, u_] := Map[If[(# > l) && (# <= u), 1, 0] &, w, {2}]
>

If this can help the discussion, on my 2 years old Mac 266 MH,  I get:


In[1]:=
d2wreal[w_, l_, u_] := Map[If[(# > l) && (# ? u), 1, 0] &, w, {2}]

In[2]:=
a = Table[Random[], {i, 1, 1000}, {j, 1, 1000}];

In[3]:=
t = Timing[d2wreal[a, 0.2, 0.4]][[1]]

Out[3]=
4.2 Second



And my poor Mac don't go through the Listable version...

It remainds me that in other circumstances, I also encountered a quite large
timing difference in 2 ways of closing several palettes, the very slower one
use too the Listable attributes. I did ask the question in an open form to the
group, without giving my own solutions, quite recently, just to see if I missed
something, but I did not get any answer. So I managed and took the less bad of
my solutions, but I'm still curious about that...


So my more general question is:
======================
Did people notice large timing difference using Listable versus Map? Who can
tell me when listable might slow down? In what circumstances?



Jacqueline Zizi



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