| What is the main difference between a script and a procedure? [message #56108] |
Wed, 03 October 2007 00:22  |
mystea
Messages: 16
Registered: October 2007
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Junior Member |
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Hello All,
I am pretty much a novice in IDL. Recently I just learned how to write/
execute a IDL script file. (i.e. @filename)
I became a little curious(or more properly, confused) about the
difference between a procedure and a script. I have my own thoughts
but would like to hear opinions from experts if possible.
As far as I can tell, a script:
1. Can't accept any arguments and can't take any extended loops.
2. It can recognize any variable that exists in the current session
because it behaves just like a a list of commands in sequence.
On the other hand, a procedure:
1. Can accept arguments, but can't recognize any variables which exist
in current IDL session.
However, I often run into the situation that I need a code which can
recognize variables in current session *as well as* taking arguments.
Is it possible to write such a code?
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| Re: What is the main difference between a script and a procedure? [message #56160 is a reply to message #56108] |
Fri, 05 October 2007 08:43  |
Jean H.
Messages: 472
Registered: July 2006
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Senior Member |
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> I don't want to use a procedure because I do want to keep z00, z05 and
> z08 after I finished plotting. They contain useful information and I
> might want to shade_surf them or print them.
Well... but you ARE keeping them!!!
What you can do is to create a function that takes q as the parameter
(or whatever), creates the variable, plot it and return your Z variable...
You can call this function from the command line
Z00 = myPlotFunct(0)
then
Z05 = myPlotFunct(0.5) etc!
If you want to use it in a program, it is fine too!
Jean
PS: always remember the rule of the least effort... if you type the same
things again and again, there is certainly a way of automating it!
> My own way of doing this task so far is:
>
> <setup.pro>
> .compile make2Darr.pro
> xaxis=5.0+0.2*findgen(200)
> yaxis=3.0+0.1*findgen(200)
>
> <qContour.pro>
> zq=make2Darr(q)
> contour, zq, xaxis, yaxis, levels=[0], overplot=overplot
>
> IDL>@setup
> IDL>q=0
> IDL>overplot=0
> IDL>@qContour
> IDL>z00=zq
> IDL>q=0.5
> IDL>overplot=1
> IDL>@qContour
> IDL>z05=zq
> ...
> ...
>
> I wonder if there a better way to accomplish this task? In the ideal
> situation, I wish I could keyin something like:
> "@qContour, 0.5, 1" to accomplish the task done by:
> IDL>overplot=1
> IDL>@qContour
> IDL>z05=zq
>
> Sincerely,
>
> Gene
>
> On Oct 3, 6:40 am, David Fanning <n...@dfanning.com> wrote:
>> mystea writes:
>>> As far as I can tell, a script:
>>> 1. Can't accept any arguments and can't take any extended loops.
>>> 2. It can recognize any variable that exists in the current session
>>> because it behaves just like a a list of commands in sequence.
>>> On the other hand, a procedure:
>>> 1. Can accept arguments, but can't recognize any variables which exist
>>> in current IDL session.
>> What you are calling a "script", most people call a
>> "batch file". This is a way to execute a series of
>> commands "as if" you were typing them at the IDL
>> command line. Since this is just about the most limited
>> way of using IDL, batch files are typically used infrequently.
>>
>> More often people will put the same commands into
>> a file and add an END statement at the end of the file.
>> This file is now a "main-level program". It must be
>> compiled before it can be executed. Normally the
>> compile and execute is done with the .RUN executive
>> command. The big advantage of main-level programs over
>> batch files, is that you can include extended loops, etc.
>> in a main-level program without all the shenanigans
>> required to get a loop to work on the IDL command line.
>>
>> As you become more sophisticated in your programming, you
>> will eventually realize that having all your variables
>> in one big pot is probably not such a great idea. (Especially
>> if you tend to name all your variables "a" to avoid a lot
>> of typing.) At that point, you might be interested in writing
>> procedures and functions (just another term for "IDL commands")
>> that do particular things for you, while at the same time,
>> keeping their internal variables from contaminating your
>> main-level working space.
>>
>> IDL uses a "pass by reference" method of getting variables
>> into and out of commands, so it is easy to write procedures
>> and functions that change main-level variables, if that is
>> your purpose. You do, in fact, have to pass the variables into
>> the procedure or function via arguments or keywords, however,
>> since all the "action" occurs on a level separate from the
>> main level. (There are ways to access main-level variables
>> from within procedures and functions that don't involve passing
>> the variables, but this is rarely done, and only by experienced
>> programmers who REALLY know what they are doing and why they are
>> doing it.)
>>
>>> However, I often run into the situation that I need a code which can
>>> recognize variables in current session *as well as* taking arguments.
>>> Is it possible to write such a code?
>> This is called "having your cake and eating it, too". It is
>> as easy to do in IDL as it is in life. :-)
>>
>> And, anyway, what could your possibly pass to a batch file
>> that the batch file didn't already know about? The only thing
>> you can pass are things that exist at the main IDL level, and
>> the batch file already has access to all of that.
>>
>> Cheers,
>>
>> David
>>
>> --
>> David Fanning, Ph.D.
>> Fanning Software Consulting, Inc.
>> Coyote's Guide to IDL Programming:http://www.dfanning.com/
>> Sepore ma de ni thui. ("Perhaps thou speakest truth.")
>
>
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| Re: What is the main difference between a script and a procedure? [message #56170 is a reply to message #56108] |
Fri, 05 October 2007 06:39 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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mystea writes:
> I wonder if there a better way to accomplish this task? In the ideal
> situation, I wish I could keyin something like:
> "@qContour, 0.5, 1" to accomplish the task done by:
> IDL>overplot=1
> IDL>@qContour
> IDL>z05=zq
Well written procedures and functions come to mind, but...
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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