MathGroup Archive 2000

[Date Index] [Thread Index] [Author Index]

Search the Archive

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


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



  • Prev by Date: Re: Laguueree polynomials
  • Next by Date: Re: Referencing Equations by Number
  • Previous by thread: Re: Fast (compiled) routine for element testing and replacement in large matrices?
  • Next by thread: Re: Fast (compiled) routine for element testing and replacement in large matrices?