| Re: Multiple values from a function? [message #20562] |
Wed, 05 July 2000 00:00 |
John-David T. Smith
Messages: 384
Registered: January 2000
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Senior Member |
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Craig Markwardt wrote:
>
> "J.D. Smith" <jdsmith@astro.cornell.edu> writes:
>>
>> void=routine_names('a',STORE=-1,val)
>>
>> Lions and tigers and bears, oh my!
>
> Pay no attention to the man behind the curtain! I still say this
> doesn't work for most cases, at least under Unix. The following is a
> simple transcript to test thes, which shows how ROUTINE_NAMES crashes
> when A is undefined, but works when A is defined. In every case that
> I tried (as noted below), the variable A needs to be defined at the
> calling level *first* before ROUTINE_NAMES(STORE=) will work.
>
> It could be that this works under v5.3, or on Windows. I don't know
> since we don't have those versions around here.
>
> Craig
>
> IDL> .run
> pro testset, name
> void = routine_names(name,store=-1,findgen(10))
> end
> % Compiled module: TESTSET.
>
> IDL> testset, 'a' ;; A is undefined here, and it doesn't work
> % ROUTINE_NAMES: Variable is undefined: a.
> % Execution halted at: TESTSET 2 /dev/tty
> % $MAIN$
> IDL> retall
> IDL> a = 1
> IDL> testset, 'a' ;; Now A is defined and it works.
> IDL> help, a
> A FLOAT = Array[10]
>
> IDL> print, !version
> { x86 linux unix 5.2.1 Jun 4 1999}
> { alpha OSF unix 5.2 Oct 30 1998}
> { x86 linux unix 5.1 Apr 13 1998}
> { alpha OSF unix 5.0 Apr 28 1997}
> { alpha OSF unix 4.0.1}
IDL> testset,'a'
IDL> print,a
0.00000 1.00000 2.00000 3.00000 4.00000 5.00000
6.00000 7.00000 8.00000 9.00000
IDL> print,!VERSION
{ x86 linux unix 5.3 Nov 11 1999}
You just need the new magic wand, version 5.3.
JD
--
J.D. Smith /*\ WORK: (607) 255-6263
Cornell University Dept. of Astronomy \*/ (607) 255-5842
304 Space Sciences Bldg. /*\ FAX: (607) 255-5875
Ithaca, NY 14853 \*/
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| Re: Multiple values from a function? [message #20563 is a reply to message #20562] |
Wed, 05 July 2000 00:00  |
Simon de Vet
Messages: 36
Registered: May 2000
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Member |
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Martin Schultz wrote:
> Simon de Vet wrote:
>>
>> [...]
>> I have managed to solve my problem, but in a way unlike anything mentioned
>> here so far.
>>
> Not true: this is exactly what I proposed.
Wah!
I had read your post, but at the time I didn't realise that it was using
structures. I later figured this out on my own, but didn't bother to re-read
the messages.
It was "keyword parameters" that threw me off...
:(
Simon
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| Re: Multiple values from a function? [message #20564 is a reply to message #20562] |
Wed, 05 July 2000 00:00 |
Craig Markwardt
Messages: 1869
Registered: November 1996
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Senior Member |
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"J.D. Smith" <jdsmith@astro.cornell.edu> writes:
>
> void=routine_names('a',STORE=-1,val)
>
> Lions and tigers and bears, oh my!
Pay no attention to the man behind the curtain! I still say this
doesn't work for most cases, at least under Unix. The following is a
simple transcript to test thes, which shows how ROUTINE_NAMES crashes
when A is undefined, but works when A is defined.� In every case that
I tried (as noted below), the variable A needs to be defined at the
calling level *first* before ROUTINE_NAMES(STORE=) will work.
It could be that this works under v5.3, or on Windows. I don't know
since we don't have those versions around here.
Craig
IDL> .run
pro testset, name
void = routine_names(name,store=-1,findgen(10))
end
% Compiled module: TESTSET.
IDL> testset, 'a' ;; A is undefined here, and it doesn't work
% ROUTINE_NAMES: Variable is undefined: a.
% Execution halted at: TESTSET 2 /dev/tty
% $MAIN$
IDL> retall
IDL> a = 1
IDL> testset, 'a' ;; Now A is defined and it works.
IDL> help, a
A FLOAT = Array[10]
IDL> print, !version
{ x86 linux unix 5.2.1 Jun 4 1999}
{ alpha OSF unix 5.2 Oct 30 1998}
{ x86 linux unix 5.1 Apr 13 1998}
{ alpha OSF unix 5.0 Apr 28 1997}
{ alpha OSF unix 4.0.1}
--
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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@cow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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| Re: Multiple values from a function? [message #20565 is a reply to message #20562] |
Wed, 05 July 2000 00:00 |
John-David T. Smith
Messages: 384
Registered: January 2000
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Senior Member |
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Martin Schultz wrote:
>
> Simon de Vet wrote:
>>
>> [...]
>> I have managed to solve my problem, but in a way unlike anything mentioned
>> here so far.
>>
> Not true: this is exactly what I proposed. I would be amazed if you
> would find a way that is entirely different (and still usable) from the
> recommendations that were provided to you (not counting some vague
> possibility of using common blocks, of course).
>
But we lowlanders should not forget the sorcerer's apprentice who scrawled this
epigram on the stone wall of his tower prison just before dissappearing forever:
void=routine_names('a',STORE=-1,val)
Lions and tigers and bears, oh my!
JD
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| Re: Multiple values from a function? [message #20566 is a reply to message #20562] |
Wed, 05 July 2000 00:00 |
Martin Schultz
Messages: 515
Registered: August 1997
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Senior Member |
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Simon de Vet wrote:
>
>
> I have managed to solve my problem, but in a way unlike anything mentioned
> here so far.
>
Not true: this is exactly what I proposed. I would be amazed if you
would find a way that is entirely different (and still usable) from the
recommendations that were provided to you (not counting some vague
possibility of using common blocks, of course).
> [...][/color]
Martin
--
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[ [[[[[[[
[[ Dr. Martin Schultz Max-Planck-Institut fuer Meteorologie [[
[[ Bundesstr. 55, 20146 Hamburg [[
[[ phone: +49 40 41173-308 [[
[[ fax: +49 40 41173-298 [[
[[ martin.schultz@dkrz.de [[
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[ [[[[[[[
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| Re: Multiple values from a function? [message #20567 is a reply to message #20562] |
Wed, 05 July 2000 00:00 |
Simon de Vet
Messages: 36
Registered: May 2000
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Member |
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Simon de Vet wrote:
> It also produces a number of other arrays which I'd like to have access
> to. Unfortunately, I have discovered that a function can only return
> one value.
I have managed to solve my problem, but in a way unlike anything mentioned
here so far.
In the end, I managed to figure out how structures work. I put all the
arrays and variables into one structure at the end of my function, and
passed this to the main program. Here, I was able to take it apart again,
and get all the original arrays and variables back.
I don't know if this is a better or worse method than those mentioned, but
it works so I'll keep using it for now.
Simon
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| Re: Multiple values from a function? [message #20570 is a reply to message #20562] |
Tue, 04 July 2000 00:00 |
meron
Messages: 51
Registered: July 1995
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Member |
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In article <3961EFA8.49657FB6@mathstat.dal.ca>, Simon de Vet <simon@mathstat.dal.ca> writes:
> I have a function that does a whole lot (it started out as an
> independent program). It works very well when returning one of it's
> calculated arrays.
>
> It also produces a number of other arrays which I'd like to have access
> to. Unfortunately, I have discovered that a function can only return
> one value.
>
> How can I get the other arrays out of it? The code is intertwined, so it
> would be hard to break into 2 or 3 independent functions.
>
You can easily return them using keyword parameters. Lets say that
your function FUN calculates 3 arrays (internally known as XARR, YARR
and ZARR) and returns XARR. Then, modify the definition of the
function to something like
Fuction FUN, ... ..., second = yarr, third = zarr
....
return, xarr
end
Now, if you'll issue a call like
u = Fun( .... ,second = v, third = w)
then after the call U will contain the calculated XARR, V will contain
YARR, w will contain ZARR. This can be extended indefinitely. Note
that neither U not V or W need to be defined at all, prior to the
call.
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: Multiple values from a function? [message #20571 is a reply to message #20570] |
Tue, 04 July 2000 00:00 |
Martin Schultz
Messages: 515
Registered: August 1997
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Senior Member |
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Simon de Vet wrote:
>
> I have a function that does a whole lot (it started out as an
> independent program). It works very well when returning one of it's
> calculated arrays.
>
> It also produces a number of other arrays which I'd like to have access
> to. Unfortunately, I have discovered that a function can only return
> one value.
>
> How can I get the other arrays out of it? The code is intertwined, so it
> would be hard to break into 2 or 3 independent functions.
>
> Concatenation of arrays is not an option, since they are all of
> different sizes. I can get around the problem by doing the calculation
> in the main level program instead of in a function, but that's a little
> ackward. Looking at the help, structures look like a possibility, but I
> don't understand how they work.
>
> Help!
>
> Simon
Second alternative: store all your results in a structure. Example:
function mything, in1, in2
sum=in1+in2
diff=in1-in2
result = { sum:sum, diff:diff }
return,result
end
You can then access the results as in:
thunder = mything(5.,20.)
print,'Sum is : ',thunder.sum,' Difference is : ',thunder.diff
One addition to Craig's answer: the parameter could also be a keyword,
e.g.
function mything, in, out=out
This is particularily recommended if you judge the output as optional.
In this case
you can use the arg_present function to determine whether output shall
be computed or not:
...
if arg_present(out) then begin
;; long-winded computation worth at least 3 trips to coffee maker
...
endif
Cheers,
Martin
--
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[ [[[[[[[
[[ Dr. Martin Schultz Max-Planck-Institut fuer Meteorologie [[
[[ Bundesstr. 55, 20146 Hamburg [[
[[ phone: +49 40 41173-308 [[
[[ fax: +49 40 41173-298 [[
[[ martin.schultz@dkrz.de [[
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[ [[[[[[[
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| Re: Multiple values from a function? [message #20572 is a reply to message #20570] |
Tue, 04 July 2000 00:00 |
Craig Markwardt
Messages: 1869
Registered: November 1996
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Senior Member |
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Simon de Vet <simon@mathstat.dal.ca> writes:
> I have a function that does a whole lot (it started out as an
> independent program). It works very well when returning one of it's
> calculated arrays.
>
> It also produces a number of other arrays which I'd like to have access
> to. Unfortunately, I have discovered that a function can only return
> one value.
>
> How can I get the other arrays out of it? The code is intertwined, so it
> would be hard to break into 2 or 3 independent functions.
> ...
The first and simple answer is, "no," you can't RETURN multiple values
like you desire.
However, the second and more useful answer is that you CAN return
values in positional or keyword parameters. IDL is pass-by-reference
in most cases, so you can simply set the parameter value to whatever
you want. I do this all the time to return subsidiary values, and it
works for both procedures and functions.
function example, in, out
out = in^2 ;; calling routine will have new value of OUT upon return
return in^3
end
Good luck,
Craig
--
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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@cow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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