comp.lang.idl-pvwave archive: archive » Use of Temporary( ) vs an Optimised Compiler

Home » Public Forums » archive » Use of Temporary( ) vs an Optimised Compiler

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: Use of Temporary( ) vs an Optimised Compiler [message #28174 is a reply to message #28130]

Tue, 27 November 2001 09:24

Pavel A. Romashkin
Messages: 531
Registered: November 2000

Senior Member

Craig Markwardt wrote:
>
>> a = 2*a + b/TEMPORARY(a)
>
> Since A appears twice on the right hand side, the compiler would need
> to be smart enough to not overwrite A after its first appearance. In
> fact, I am not sure that IDL makes any guarantees about order of
> evaluation and side effects. Isn't it possible that the TEMPORARY()
> gets called before the first A is evaluated?

I recently had to think about memory allocation in IDL for the first
time as I had to use large arays (well, some 4E+7 points, astronomy guys
don't laugh).
In my case it appeared faster (and sometimes the only way possible to
avoid infufficient memory errors) to split the above expression

a = 2*a +b/temporary(a)

into

a = 2*temporary(a)
a = 2*b/temporary(a)

It takes a while even to do math on xE+7 points, and allocating arrays
further slows things down.
In this simple case, this is easy to do, but some expressions were quite
hard to split like this. There are probably better ways.
Cheers,
Pavel

Report message to a moderator

[Message index]

		Use of Temporary( ) vs an Optimised Compiler By: Martin Downing on Mon, 26 November 2001 07:38
		Re: Use of Temporary( ) vs an Optimised Compiler By: Pavel A. Romashkin on Tue, 27 November 2001 09:24
		Re: Use of Temporary( ) vs an Optimised Compiler By: Paul van Delst on Tue, 27 November 2001 10:46
		Re: Use of Temporary( ) vs an Optimised Compiler By: Martin Downing on Tue, 27 November 2001 02:42
		Re: Use of Temporary( ) vs an Optimised Compiler By: Craig Markwardt on Mon, 26 November 2001 21:42
		Re: Use of Temporary( ) vs an Optimised Compiler By: Liam E. Gumley on Tue, 27 November 2001 11:13

Previous Topic:	Re: removing old IDL versions
Next Topic:	Automatic truncation of trailing dimension.....

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Wed Oct 08 15:43:55 PDT 2025

Total time taken to generate the page: 0.00423 seconds