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MathGroup Archive 2005

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Re: Timing of looping operators

  • To: mathgroup at
  • Subject: [mg62420] Re: [mg62416] Timing of looping operators
  • From: "Hermann Schmitt" <schmitther at>
  • Date: Wed, 23 Nov 2005 06:27:31 -0500 (EST)
  • References: <>
  • Sender: owner-wri-mathgroup at

Hello Daniel,
loops are normally more efficient then recursive function calls, because in
function calls more temporary variables have to be created.
In my oo system I first tried recursive function calls, but then changed to
Hermann Schmitt
----- Original Message -----
From: "dh" <dh at>
To: mathgroup at
Subject: [mg62420] [mg62416] Timing of looping operators

> Hello,
> The Mathematica gospel tells you that you should NOT use loops because
> it is inefficient.
> Well consider the following examples and their times:
> n=10^6;
> d=Table[i,{i,n}];
> fun[x_]:=x;
> a)  Timing[fun & /@ d;]       needs 0.8 sec
> b)  Timing[Scan[fun, d]]      needs 1 second
> c)  Timing[Do[f[i], {i, n}];] needs 0.7 sec
> a) applies the function and creates a new list. b) does not create a new
> list -- but it is slower! And finally c) the loop is fastest!!!
> If you change the function to: f[x_]:=x^2, the times are even more
> 0.8, 2.4, 0.7
> it seems like in a and c the function evaluation takes negliable time
> compared to the loop construct, but not so in b.
> has anybody an explanation???
> Daniel

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