| Re: loop limit ??? [message #53579] |
Wed, 18 April 2007 15:28 |
mmeron
Messages: 44
Registered: October 2003
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Member |
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In article <1176929681.182929.291930@q75g2000hsh.googlegroups.com>, kostis <kostiskaz@gmail.com> writes:
> i wouldnt expect that IDL has a limit for loops !!
> trying a loop of 50.000 steps i got the message:
>
> % Compiled module: TRAJECTORY.
> % Loop limit expression too large for loop variable type.
> <LONG ( 49999)>.
> % Execution halted at: TRAJECTORY 16 /home/kostis/PROJECT
> LARMOR/dipole/trajectory.pro
> % $MAIN$
>
> Why is this?
> This means i cant have bigger loops... or is there a trick??
>
You can have much larger loops, just be careful about the indexing.
In the expression
for i = a, b do ....
the type of the loop variable is determined by the type of a
(regardless of what b is). So, if you write
for i = 0, 50000
or even
for i = 0, 50000l
the loop variable will be a standard (aka "short") integer and these
are limited to 2^15 - 1, i.e. 32767. But if you'll write
for i = 0l, 50000
the loop variable is of type LONG and the limit is at 2^31 - 1, more
then 2 billion. If that's not enough you can use LONG64, at which
point it'll probably be the longevity of the computer that'll
determine the limit
Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"
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| Re: loop limit ??? [message #53580 is a reply to message #53579] |
Wed, 18 April 2007 15:06  |
Michael Galloy
Messages: 1114
Registered: April 2006
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Senior Member |
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On Apr 18, 3:45 pm, Gianguido Cianci <gianguido.cia...@gmail.com>
wrote:
> Or you could get into the habit of typing
>
> Compile_Opt IDL2
>
> at the beginning of our programs and never worry about it again.
> ('downside' is you are forced to use [] for arrays and () only for
> functions)
>
> Gianguido
I don't consider it a downside, but if you only want the default
integer to be 32 bit then use
compile_opt defint32
instead of idl2 (which is just a convenience for both defint32 and
strictarr).
Mike
--
www.michaelgalloy.com
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| Re: loop limit ??? [message #53582 is a reply to message #53580] |
Wed, 18 April 2007 14:45 |
cgguido
Messages: 195
Registered: August 2005
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Senior Member |
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On Apr 18, 4:54 pm, kostis <kostis...@gmail.com> wrote:
> i wouldnt expect that IDL has a limit for loops !!
> trying a loop of 50.000 steps i got the message:
>
> % Compiled module: TRAJECTORY.
> % Loop limit expression too large for loop variable type.
> <LONG ( 49999)>.
> % Execution halted at: TRAJECTORY 16 /home/kostis/PROJECT
> LARMOR/dipole/trajectory.pro
> % $MAIN$
>
> Why is this?
> This means i cant have bigger loops... or is there a trick??
>
> Thanx...
Or you could get into the habit of typing
Compile_Opt IDL2
at the beginning of our programs and never worry about it again.
('downside' is you are forced to use [] for arrays and () only for
functions)
Gianguido
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| Re: loop limit ??? [message #53583 is a reply to message #53582] |
Wed, 18 April 2007 14:02 |
Foldy Lajos
Messages: 268
Registered: October 2001
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Senior Member |
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On Wed, 18 Apr 2007, kostis wrote:
> i wouldnt expect that IDL has a limit for loops !!
> trying a loop of 50.000 steps i got the message:
>
> % Compiled module: TRAJECTORY.
> % Loop limit expression too large for loop variable type.
> <LONG ( 49999)>.
> % Execution halted at: TRAJECTORY 16 /home/kostis/PROJECT
> LARMOR/dipole/trajectory.pro
> % $MAIN$
>
> Why is this?
> This means i cant have bigger loops... or is there a trick??
>
IDL> for i=0,49999 do begin & endfor
% Loop limit expression too large for loop variable type.
<LONG ( 49999)>.
% Execution halted at: $MAIN$
0 is of type INT (default integer), whose max. value is 32767.
Use 0l (LONG) instead.
regards,
lajos
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| Re: loop limit ??? [message #53584 is a reply to message #53583] |
Wed, 18 April 2007 14:12 |
Michael Galloy
Messages: 1114
Registered: April 2006
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Senior Member |
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On Apr 18, 2:54 pm, kostis <kostis...@gmail.com> wrote:
> i wouldnt expect that IDL has a limit for loops !!
> trying a loop of 50.000 steps i got the message:
>
> % Compiled module: TRAJECTORY.
> % Loop limit expression too large for loop variable type.
> <LONG ( 49999)>.
> % Execution halted at: TRAJECTORY 16 /home/kostis/PROJECT
> LARMOR/dipole/trajectory.pro
> % $MAIN$
>
> Why is this?
> This means i cant have bigger loops... or is there a trick??
There's a "trick". A FOR loop variable gets it type from the "start"
value of the loop and it doesn't change in the course of the loop.
So, (note the 0L -- it's the "trick"):
for i = 0L, 50000L do begin
; stuff here
endfor
should do it for you.
Mike
--
www.michaelgalloy.com
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