On Monday, July 9, 2012 7:36:00 AM UTC-10, Mike Galloy wrote:
> On 7/6/12 10:28 PM, Thesource007 wrote:
> > On Friday, July 6, 2012 8:42:48 PM UTC-7, Craig Markwardt wrote:
> >> On Friday, July 6, 2012 5:43:30 PM UTC-4, Thesource007 wrote:
> >>> Hi all.
> >>> This is my problem. I have two IDL procedures
> >>> hr2altaz, hour, dec, alt, az -- which takes the HA and DEC and
> >>> converts it to ALT and AZ
> >>> altaz2hr, hour, dec, alt, az -- which takes ALT and AZ, and converts
> >>> it to HA and DEC.
> >>>
> >>> What I need to do, is to begin with a certain HA and DEC, execute
> >>> hr2altaz, which will give me the ALT and AZ, and then take those two
> >>> outputs to execute altaz2hr, which will convert themj back to HA and
> >>> DEC, and then repeat the process many times (say 100).
> >>> The purpose being to compare the initial HA, DEC to the final (after
> >>> 100 reps) HA, DEC.
> >>> Is there a simple way to do this? Or I just have to use an input file
> >>> and loops?
> >>
> >> Applying the function and its inverse: yes, just use a loop. The overhead of executing a loop 100 times is minimal.
> >>
> >> "An input file" : that's up to you. But you can always read your values into an array once at the beginning.
> >>
> >> Craig
> >
> > Ok. But now the question is... how do I "transfer" the output of one procedure to be the input of the other? I dont have a clue of how to do that.
> > Thank you
> >
>
> From what I understand, you just need to do this:
>
> for i = 0, 99 do begin
> hr2altaz, orig_hour, orig_dec, alt, az
> altaz2hr, hour, dec, alt, az
> ; compare orig_hour/orig_dec to hour/dec
> endfor
>
> IDL passes "named variables" like orig_hour, orig_dec, etc. by
> reference, meaning changes to them inside the routine are passed out of
> the routine. So when alt/az are modified in hr2altaz, the new values are
> passed into altaz2hr.
>
> On the other hand, expressions like orig_hour[*], alt[0], my_struct.x,
> etc. are passed by value and modifications to them inside a routine are
> only local to that routine.
>
> Mike
> --
> Michael Galloy
> www.michaelgalloy.com
> Modern IDL: A Guide to IDL Programming (http://modernidl.idldev.com)
> Research Mathematician
> Tech-X Corporation
Thank you for your response. But now I have a question.
How would I input the firts HA and DEC, and where should I write the code? Should be a new procedure?
What I did was to create a new procedure like this
pro doarun, hour, dec
for i = 0, 99 do begin
hr2altaz, hour, dec, alt, az
altaz2hr, hour, dec, alt, az
endfor
END
It seems to work, but I have some problems.
The numbers used to change a bit. Something like the original inputs would be dorun, 18.5666, -16.7313
and the last hour and dec(after 100 reps) would be 18.566597 & -16.730573. Good.
Now what I wanted to do is to minimize this change, so I changed my codes to calculate in double precision. Now, for every hour, dec, alt, az, they just repeat 100 times, without any change. I dont know if this is suppose to happen, or maybe every time the loop runs, it takes my initial inputs again and again, which I dont think so because the numbers used to change (they were FLOAT before, now they are DOUBLE). Could you tell me if what I did was correct? I mean, I wanted to minimize the difference between the original inputs and outputs, but now they dont change at all. I dont know if I fixed it or I just messed it up.
Thank you for your help
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