| Re: is this a bug in IDL? [message #37463 is a reply to message #37376] |
Tue, 16 December 2003 13:17  |
aramisgm
Messages: 4
Registered: December 2003
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Junior Member |
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I've used index, but I'd forgotten about it. Thanks for the reminder.
Ah, the & means for each iteration do an if-then block, then do the
two following statements (as opposed to tying together the three
statements as the then part of the if-then block) -- the scope for the
& is slightly different than in, say, Java. However, now there is a
new problem. The entire array should get zeroed out if the snippet
below is what is happening. . . (five minutes and a phone call later)
indeed it is! To me this seems to be a non-standard usage of &, but
that's what I get for being trained in c and its descendants :+) The
three statements go into a do-begin-end block, problem solved.
Thank you gentlemen. Enlightenment received.
Aramis Martinez
Wonko@wonkology.org (Alex Schuster) wrote in message news:<8zysEJaud8B@wonkology.org>...
> aramisgm@hotmail.com (Aramis Martinez) wrote:
>
>> k=0
>> for i=0,8759 do begin
>> x=vbs(2,i)
>> if x gt 0.0 then k=k+1 & x=0 & vbs(2,i)=x
>> endfor
>> print, k
>
> Which is the same as:
>
> k=0
> for i=0,8759 do begin
> x=vbs(2,i)
> if x gt 0.0 then k=k+1
> x=0
> vbs(2,i)=x
> endfor
> print, k
>
>
>> 1) How would you vectorize this? I tried a few things that I could
>> remember from my work this summer, but four months of quantum
>> mechanics wipes a lot from memory :)
>
> This should do:
>
> index = where( vbs[ 2, lindgen( 8760 ) ] gt 0, k )
> if k gt 0 then vbs[ 2, index ] = 0
>
>
> [...]
>
>> Is this a bug? as far as I can tell, the statements are logically
>> identical since an &'s behavior should never vary, so what in the guts
>> of IDL would make these statements be different? Is there some rule
>> kicking in here that's not so obvious but makes this behavior to be
>> expected? Would parenthesis around the THEN block make these identical
>> in IDL? The environment is either IDL 6 on Red Hat 9 or IDL 5.1 on
>> Red Hat 8.1.
>
> Using & ist the same as wrting the next statement in another line. You
> need to use begin and endif statements.
>
> Alex
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